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+/**
+ * Firebase Realtime Database
+ *
+ * @packageDocumentation
+ */
+import { FirebaseApp } from '@firebase/app';
+import { EmulatorMockTokenOptions } from '@firebase/util';
+
+/**
+ * Gets a `Reference` for the location at the specified relative path.
+ *
+ * The relative path can either be a simple child name (for example, "ada") or
+ * a deeper slash-separated path (for example, "ada/name/first").
+ *
+ * @param parent - The parent location.
+ * @param path - A relative path from this location to the desired child
+ *   location.
+ * @returns The specified child location.
+ */
+export declare function child(parent: DatabaseReference, path: string): DatabaseReference;
+/**
+ * Modify the provided instance to communicate with the Realtime Database
+ * emulator.
+ *
+ * <p>Note: This method must be called before performing any other operation.
+ *
+ * @param db - The instance to modify.
+ * @param host - The emulator host (ex: localhost)
+ * @param port - The emulator port (ex: 8080)
+ * @param options.mockUserToken - the mock auth token to use for unit testing Security Rules
+ */
+export declare function connectDatabaseEmulator(db: Database, host: string, port: number, options?: {
+    mockUserToken?: EmulatorMockTokenOptions | string;
+}): void;
+/**
+ * Class representing a Firebase Realtime Database.
+ */
+export declare class Database {
+    /** The {@link @firebase/app#FirebaseApp} associated with this Realtime Database instance. */
+    readonly app: FirebaseApp;
+    /** Represents a `Database` instance. */
+    readonly 'type' = "database";
+    private constructor();
+}
+/**
+ * A `DatabaseReference` represents a specific location in your Database and can be used
+ * for reading or writing data to that Database location.
+ *
+ * You can reference the root or child location in your Database by calling
+ * `ref()` or `ref("child/path")`.
+ *
+ * Writing is done with the `set()` method and reading can be done with the
+ * `on*()` method. See {@link
+ * https://firebase.google.com/docs/database/web/read-and-write}
+ */
+export declare interface DatabaseReference extends Query {
+    /**
+     * The last part of the `DatabaseReference`'s path.
+     *
+     * For example, `"ada"` is the key for
+     * `https://<DATABASE_NAME>.firebaseio.com/users/ada`.
+     *
+     * The key of a root `DatabaseReference` is `null`.
+     */
+    readonly key: string | null;
+    /**
+     * The parent location of a `DatabaseReference`.
+     *
+     * The parent of a root `DatabaseReference` is `null`.
+     */
+    readonly parent: DatabaseReference | null;
+    /** The root `DatabaseReference` of the Database. */
+    readonly root: DatabaseReference;
+}
+/**
+ * A `DataSnapshot` contains data from a Database location.
+ *
+ * Any time you read data from the Database, you receive the data as a
+ * `DataSnapshot`. A `DataSnapshot` is passed to the event callbacks you attach
+ * with `on()` or `once()`. You can extract the contents of the snapshot as a
+ * JavaScript object by calling the `val()` method. Alternatively, you can
+ * traverse into the snapshot by calling `child()` to return child snapshots
+ * (which you could then call `val()` on).
+ *
+ * A `DataSnapshot` is an efficiently generated, immutable copy of the data at
+ * a Database location. It cannot be modified and will never change (to modify
+ * data, you always call the `set()` method on a `Reference` directly).
+ */
+export declare class DataSnapshot {
+    /**
+     * The location of this DataSnapshot.
+     */
+    readonly ref: DatabaseReference;
+    private constructor();
+    /**
+     * Gets the priority value of the data in this `DataSnapshot`.
+     *
+     * Applications need not use priority but can order collections by
+     * ordinary properties (see
+     * {@link https://firebase.google.com/docs/database/web/lists-of-data#sorting_and_filtering_data |Sorting and filtering data}
+     * ).
+     */
+    get priority(): string | number | null;
+    /**
+     * The key (last part of the path) of the location of this `DataSnapshot`.
+     *
+     * The last token in a Database location is considered its key. For example,
+     * "ada" is the key for the /users/ada/ node. Accessing the key on any
+     * `DataSnapshot` will return the key for the location that generated it.
+     * However, accessing the key on the root URL of a Database will return
+     * `null`.
+     */
+    get key(): string | null;
+    /** Returns the number of child properties of this `DataSnapshot`. */
+    get size(): number;
+    /**
+     * Gets another `DataSnapshot` for the location at the specified relative path.
+     *
+     * Passing a relative path to the `child()` method of a DataSnapshot returns
+     * another `DataSnapshot` for the location at the specified relative path. The
+     * relative path can either be a simple child name (for example, "ada") or a
+     * deeper, slash-separated path (for example, "ada/name/first"). If the child
+     * location has no data, an empty `DataSnapshot` (that is, a `DataSnapshot`
+     * whose value is `null`) is returned.
+     *
+     * @param path - A relative path to the location of child data.
+     */
+    child(path: string): DataSnapshot;
+    /**
+     * Returns true if this `DataSnapshot` contains any data. It is slightly more
+     * efficient than using `snapshot.val() !== null`.
+     */
+    exists(): boolean;
+    /**
+     * Exports the entire contents of the DataSnapshot as a JavaScript object.
+     *
+     * The `exportVal()` method is similar to `val()`, except priority information
+     * is included (if available), making it suitable for backing up your data.
+     *
+     * @returns The DataSnapshot's contents as a JavaScript value (Object,
+     *   Array, string, number, boolean, or `null`).
+     */
+    exportVal(): any;
+    /**
+     * Enumerates the top-level children in the `IteratedDataSnapshot`.
+     *
+     * Because of the way JavaScript objects work, the ordering of data in the
+     * JavaScript object returned by `val()` is not guaranteed to match the
+     * ordering on the server nor the ordering of `onChildAdded()` events. That is
+     * where `forEach()` comes in handy. It guarantees the children of a
+     * `DataSnapshot` will be iterated in their query order.
+     *
+     * If no explicit `orderBy*()` method is used, results are returned
+     * ordered by key (unless priorities are used, in which case, results are
+     * returned by priority).
+     *
+     * @param action - A function that will be called for each child DataSnapshot.
+     * The callback can return true to cancel further enumeration.
+     * @returns true if enumeration was canceled due to your callback returning
+     * true.
+     */
+    forEach(action: (child: IteratedDataSnapshot) => boolean | void): boolean;
+    /**
+     * Returns true if the specified child path has (non-null) data.
+     *
+     * @param path - A relative path to the location of a potential child.
+     * @returns `true` if data exists at the specified child path; else
+     *  `false`.
+     */
+    hasChild(path: string): boolean;
+    /**
+     * Returns whether or not the `DataSnapshot` has any non-`null` child
+     * properties.
+     *
+     * You can use `hasChildren()` to determine if a `DataSnapshot` has any
+     * children. If it does, you can enumerate them using `forEach()`. If it
+     * doesn't, then either this snapshot contains a primitive value (which can be
+     * retrieved with `val()`) or it is empty (in which case, `val()` will return
+     * `null`).
+     *
+     * @returns true if this snapshot has any children; else false.
+     */
+    hasChildren(): boolean;
+    /**
+     * Returns a JSON-serializable representation of this object.
+     */
+    toJSON(): object | null;
+    /**
+     * Extracts a JavaScript value from a `DataSnapshot`.
+     *
+     * Depending on the data in a `DataSnapshot`, the `val()` method may return a
+     * scalar type (string, number, or boolean), an array, or an object. It may
+     * also return null, indicating that the `DataSnapshot` is empty (contains no
+     * data).
+     *
+     * @returns The DataSnapshot's contents as a JavaScript value (Object,
+     *   Array, string, number, boolean, or `null`).
+     */
+    val(): any;
+}
+export { EmulatorMockTokenOptions };
+/**
+ * Logs debugging information to the console.
+ *
+ * @param enabled - Enables logging if `true`, disables logging if `false`.
+ * @param persistent - Remembers the logging state between page refreshes if
+ * `true`.
+ */
+export declare function enableLogging(enabled: boolean, persistent?: boolean): any;
+/**
+ * Logs debugging information to the console.
+ *
+ * @param logger - A custom logger function to control how things get logged.
+ */
+export declare function enableLogging(logger: (message: string) => unknown): any;
+/**
+ * Creates a `QueryConstraint` with the specified ending point.
+ *
+ * Using `startAt()`, `startAfter()`, `endBefore()`, `endAt()` and `equalTo()`
+ * allows you to choose arbitrary starting and ending points for your queries.
+ *
+ * The ending point is inclusive, so children with exactly the specified value
+ * will be included in the query. The optional key argument can be used to
+ * further limit the range of the query. If it is specified, then children that
+ * have exactly the specified value must also have a key name less than or equal
+ * to the specified key.
+ *
+ * You can read more about `endAt()` in
+ * {@link https://firebase.google.com/docs/database/web/lists-of-data#filtering_data | Filtering data}.
+ *
+ * @param value - The value to end at. The argument type depends on which
+ * `orderBy*()` function was used in this query. Specify a value that matches
+ * the `orderBy*()` type. When used in combination with `orderByKey()`, the
+ * value must be a string.
+ * @param key - The child key to end at, among the children with the previously
+ * specified priority. This argument is only allowed if ordering by child,
+ * value, or priority.
+ */
+export declare function endAt(value: number | string | boolean | null, key?: string): QueryConstraint;
+/**
+ * Creates a `QueryConstraint` with the specified ending point (exclusive).
+ *
+ * Using `startAt()`, `startAfter()`, `endBefore()`, `endAt()` and `equalTo()`
+ * allows you to choose arbitrary starting and ending points for your queries.
+ *
+ * The ending point is exclusive. If only a value is provided, children
+ * with a value less than the specified value will be included in the query.
+ * If a key is specified, then children must have a value less than or equal
+ * to the specified value and a key name less than the specified key.
+ *
+ * @param value - The value to end before. The argument type depends on which
+ * `orderBy*()` function was used in this query. Specify a value that matches
+ * the `orderBy*()` type. When used in combination with `orderByKey()`, the
+ * value must be a string.
+ * @param key - The child key to end before, among the children with the
+ * previously specified priority. This argument is only allowed if ordering by
+ * child, value, or priority.
+ */
+export declare function endBefore(value: number | string | boolean | null, key?: string): QueryConstraint;
+/**
+ * Creates a `QueryConstraint` that includes children that match the specified
+ * value.
+ *
+ * Using `startAt()`, `startAfter()`, `endBefore()`, `endAt()` and `equalTo()`
+ * allows you to choose arbitrary starting and ending points for your queries.
+ *
+ * The optional key argument can be used to further limit the range of the
+ * query. If it is specified, then children that have exactly the specified
+ * value must also have exactly the specified key as their key name. This can be
+ * used to filter result sets with many matches for the same value.
+ *
+ * You can read more about `equalTo()` in
+ * {@link https://firebase.google.com/docs/database/web/lists-of-data#filtering_data | Filtering data}.
+ *
+ * @param value - The value to match for. The argument type depends on which
+ * `orderBy*()` function was used in this query. Specify a value that matches
+ * the `orderBy*()` type. When used in combination with `orderByKey()`, the
+ * value must be a string.
+ * @param key - The child key to start at, among the children with the
+ * previously specified priority. This argument is only allowed if ordering by
+ * child, value, or priority.
+ */
+export declare function equalTo(value: number | string | boolean | null, key?: string): QueryConstraint;
+/**
+ * One of the following strings: "value", "child_added", "child_changed",
+ * "child_removed", or "child_moved."
+ */
+export declare type EventType = 'value' | 'child_added' | 'child_changed' | 'child_moved' | 'child_removed';
+/* Excluded from this release type: _FirebaseService */
+/**
+ * Force the use of longPolling instead of websockets. This will be ignored if websocket protocol is used in databaseURL.
+ */
+export declare function forceLongPolling(): void;
+/**
+ * Force the use of websockets instead of longPolling.
+ */
+export declare function forceWebSockets(): void;
+/**
+ * Gets the most up-to-date result for this query.
+ *
+ * @param query - The query to run.
+ * @returns A `Promise` which resolves to the resulting DataSnapshot if a value is
+ * available, or rejects if the client is unable to return a value (e.g., if the
+ * server is unreachable and there is nothing cached).
+ */
+export declare function get(query: Query): Promise<DataSnapshot>;
+/**
+ * Returns the instance of the Realtime Database SDK that is associated with the provided
+ * {@link @firebase/app#FirebaseApp}. Initializes a new instance with default settings if
+ * no instance exists or if the existing instance uses a custom database URL.
+ *
+ * @param app - The {@link @firebase/app#FirebaseApp} instance that the returned Realtime
+ * Database instance is associated with.
+ * @param url - The URL of the Realtime Database instance to connect to. If not
+ * provided, the SDK connects to the default instance of the Firebase App.
+ * @returns The `Database` instance of the provided app.
+ */
+export declare function getDatabase(app?: FirebaseApp, url?: string): Database;
+/**
+ * Disconnects from the server (all Database operations will be completed
+ * offline).
+ *
+ * The client automatically maintains a persistent connection to the Database
+ * server, which will remain active indefinitely and reconnect when
+ * disconnected. However, the `goOffline()` and `goOnline()` methods may be used
+ * to control the client connection in cases where a persistent connection is
+ * undesirable.
+ *
+ * While offline, the client will no longer receive data updates from the
+ * Database. However, all Database operations performed locally will continue to
+ * immediately fire events, allowing your application to continue behaving
+ * normally. Additionally, each operation performed locally will automatically
+ * be queued and retried upon reconnection to the Database server.
+ *
+ * To reconnect to the Database and begin receiving remote events, see
+ * `goOnline()`.
+ *
+ * @param db - The instance to disconnect.
+ */
+export declare function goOffline(db: Database): void;
+/**
+ * Reconnects to the server and synchronizes the offline Database state
+ * with the server state.
+ *
+ * This method should be used after disabling the active connection with
+ * `goOffline()`. Once reconnected, the client will transmit the proper data
+ * and fire the appropriate events so that your client "catches up"
+ * automatically.
+ *
+ * @param db - The instance to reconnect.
+ */
+export declare function goOnline(db: Database): void;
+/**
+ * Returns a placeholder value that can be used to atomically increment the
+ * current database value by the provided delta.
+ *
+ * @param delta - the amount to modify the current value atomically.
+ * @returns A placeholder value for modifying data atomically server-side.
+ */
+export declare function increment(delta: number): object;
+/* Excluded from this release type: _initStandalone */
+/**
+ * Represents a child snapshot of a `Reference` that is being iterated over. The key will never be undefined.
+ */
+export declare interface IteratedDataSnapshot extends DataSnapshot {
+    key: string;
+}
+/**
+ * Creates a new `QueryConstraint` that if limited to the first specific number
+ * of children.
+ *
+ * The `limitToFirst()` method is used to set a maximum number of children to be
+ * synced for a given callback. If we set a limit of 100, we will initially only
+ * receive up to 100 `child_added` events. If we have fewer than 100 messages
+ * stored in our Database, a `child_added` event will fire for each message.
+ * However, if we have over 100 messages, we will only receive a `child_added`
+ * event for the first 100 ordered messages. As items change, we will receive
+ * `child_removed` events for each item that drops out of the active list so
+ * that the total number stays at 100.
+ *
+ * You can read more about `limitToFirst()` in
+ * {@link https://firebase.google.com/docs/database/web/lists-of-data#filtering_data | Filtering data}.
+ *
+ * @param limit - The maximum number of nodes to include in this query.
+ */
+export declare function limitToFirst(limit: number): QueryConstraint;
+/**
+ * Creates a new `QueryConstraint` that is limited to return only the last
+ * specified number of children.
+ *
+ * The `limitToLast()` method is used to set a maximum number of children to be
+ * synced for a given callback. If we set a limit of 100, we will initially only
+ * receive up to 100 `child_added` events. If we have fewer than 100 messages
+ * stored in our Database, a `child_added` event will fire for each message.
+ * However, if we have over 100 messages, we will only receive a `child_added`
+ * event for the last 100 ordered messages. As items change, we will receive
+ * `child_removed` events for each item that drops out of the active list so
+ * that the total number stays at 100.
+ *
+ * You can read more about `limitToLast()` in
+ * {@link https://firebase.google.com/docs/database/web/lists-of-data#filtering_data | Filtering data}.
+ *
+ * @param limit - The maximum number of nodes to include in this query.
+ */
+export declare function limitToLast(limit: number): QueryConstraint;
+/** An options objects that can be used to customize a listener. */
+export declare interface ListenOptions {
+    /** Whether to remove the listener after its first invocation. */
+    readonly onlyOnce?: boolean;
+}
+/**
+ * Detaches a callback previously attached with the corresponding `on*()` (`onValue`, `onChildAdded`) listener.
+ * Note: This is not the recommended way to remove a listener. Instead, please use the returned callback function from
+ * the respective `on*` callbacks.
+ *
+ * Detach a callback previously attached with `on*()`. Calling `off()` on a parent listener
+ * will not automatically remove listeners registered on child nodes, `off()`
+ * must also be called on any child listeners to remove the callback.
+ *
+ * If a callback is not specified, all callbacks for the specified eventType
+ * will be removed. Similarly, if no eventType is specified, all callbacks
+ * for the `Reference` will be removed.
+ *
+ * Individual listeners can also be removed by invoking their unsubscribe
+ * callbacks.
+ *
+ * @param query - The query that the listener was registered with.
+ * @param eventType - One of the following strings: "value", "child_added",
+ * "child_changed", "child_removed", or "child_moved." If omitted, all callbacks
+ * for the `Reference` will be removed.
+ * @param callback - The callback function that was passed to `on()` or
+ * `undefined` to remove all callbacks.
+ */
+export declare function off(query: Query, eventType?: EventType, callback?: (snapshot: DataSnapshot, previousChildName?: string | null) => unknown): void;
+/**
+ * Listens for data changes at a particular location.
+ *
+ * This is the primary way to read data from a Database. Your callback
+ * will be triggered for the initial data and again whenever the data changes.
+ * Invoke the returned unsubscribe callback to stop receiving updates. See
+ * {@link https://firebase.google.com/docs/database/web/retrieve-data | Retrieve Data on the Web}
+ * for more details.
+ *
+ * An `onChildAdded` event will be triggered once for each initial child at this
+ * location, and it will be triggered again every time a new child is added. The
+ * `DataSnapshot` passed into the callback will reflect the data for the
+ * relevant child. For ordering purposes, it is passed a second argument which
+ * is a string containing the key of the previous sibling child by sort order,
+ * or `null` if it is the first child.
+ *
+ * @param query - The query to run.
+ * @param callback - A callback that fires when the specified event occurs.
+ * The callback will be passed a DataSnapshot and a string containing the key of
+ * the previous child, by sort order, or `null` if it is the first child.
+ * @param cancelCallback - An optional callback that will be notified if your
+ * event subscription is ever canceled because your client does not have
+ * permission to read this data (or it had permission but has now lost it).
+ * This callback will be passed an `Error` object indicating why the failure
+ * occurred.
+ * @returns A function that can be invoked to remove the listener.
+ */
+export declare function onChildAdded(query: Query, callback: (snapshot: DataSnapshot, previousChildName?: string | null) => unknown, cancelCallback?: (error: Error) => unknown): Unsubscribe;
+/**
+ * Listens for data changes at a particular location.
+ *
+ * This is the primary way to read data from a Database. Your callback
+ * will be triggered for the initial data and again whenever the data changes.
+ * Invoke the returned unsubscribe callback to stop receiving updates. See
+ * {@link https://firebase.google.com/docs/database/web/retrieve-data | Retrieve Data on the Web}
+ * for more details.
+ *
+ * An `onChildAdded` event will be triggered once for each initial child at this
+ * location, and it will be triggered again every time a new child is added. The
+ * `DataSnapshot` passed into the callback will reflect the data for the
+ * relevant child. For ordering purposes, it is passed a second argument which
+ * is a string containing the key of the previous sibling child by sort order,
+ * or `null` if it is the first child.
+ *
+ * @param query - The query to run.
+ * @param callback - A callback that fires when the specified event occurs.
+ * The callback will be passed a DataSnapshot and a string containing the key of
+ * the previous child, by sort order, or `null` if it is the first child.
+ * @param options - An object that can be used to configure `onlyOnce`, which
+ * then removes the listener after its first invocation.
+ * @returns A function that can be invoked to remove the listener.
+ */
+export declare function onChildAdded(query: Query, callback: (snapshot: DataSnapshot, previousChildName: string | null) => unknown, options: ListenOptions): Unsubscribe;
+/**
+ * Listens for data changes at a particular location.
+ *
+ * This is the primary way to read data from a Database. Your callback
+ * will be triggered for the initial data and again whenever the data changes.
+ * Invoke the returned unsubscribe callback to stop receiving updates. See
+ * {@link https://firebase.google.com/docs/database/web/retrieve-data | Retrieve Data on the Web}
+ * for more details.
+ *
+ * An `onChildAdded` event will be triggered once for each initial child at this
+ * location, and it will be triggered again every time a new child is added. The
+ * `DataSnapshot` passed into the callback will reflect the data for the
+ * relevant child. For ordering purposes, it is passed a second argument which
+ * is a string containing the key of the previous sibling child by sort order,
+ * or `null` if it is the first child.
+ *
+ * @param query - The query to run.
+ * @param callback - A callback that fires when the specified event occurs.
+ * The callback will be passed a DataSnapshot and a string containing the key of
+ * the previous child, by sort order, or `null` if it is the first child.
+ * @param cancelCallback - An optional callback that will be notified if your
+ * event subscription is ever canceled because your client does not have
+ * permission to read this data (or it had permission but has now lost it).
+ * This callback will be passed an `Error` object indicating why the failure
+ * occurred.
+ * @param options - An object that can be used to configure `onlyOnce`, which
+ * then removes the listener after its first invocation.
+ * @returns A function that can be invoked to remove the listener.
+ */
+export declare function onChildAdded(query: Query, callback: (snapshot: DataSnapshot, previousChildName: string | null) => unknown, cancelCallback: (error: Error) => unknown, options: ListenOptions): Unsubscribe;
+/**
+ * Listens for data changes at a particular location.
+ *
+ * This is the primary way to read data from a Database. Your callback
+ * will be triggered for the initial data and again whenever the data changes.
+ * Invoke the returned unsubscribe callback to stop receiving updates. See
+ * {@link https://firebase.google.com/docs/database/web/retrieve-data | Retrieve Data on the Web}
+ * for more details.
+ *
+ * An `onChildChanged` event will be triggered when the data stored in a child
+ * (or any of its descendants) changes. Note that a single `child_changed` event
+ * may represent multiple changes to the child. The `DataSnapshot` passed to the
+ * callback will contain the new child contents. For ordering purposes, the
+ * callback is also passed a second argument which is a string containing the
+ * key of the previous sibling child by sort order, or `null` if it is the first
+ * child.
+ *
+ * @param query - The query to run.
+ * @param callback - A callback that fires when the specified event occurs.
+ * The callback will be passed a DataSnapshot and a string containing the key of
+ * the previous child, by sort order, or `null` if it is the first child.
+ * @param cancelCallback - An optional callback that will be notified if your
+ * event subscription is ever canceled because your client does not have
+ * permission to read this data (or it had permission but has now lost it).
+ * This callback will be passed an `Error` object indicating why the failure
+ * occurred.
+ * @returns A function that can be invoked to remove the listener.
+ */
+export declare function onChildChanged(query: Query, callback: (snapshot: DataSnapshot, previousChildName: string | null) => unknown, cancelCallback?: (error: Error) => unknown): Unsubscribe;
+/**
+ * Listens for data changes at a particular location.
+ *
+ * This is the primary way to read data from a Database. Your callback
+ * will be triggered for the initial data and again whenever the data changes.
+ * Invoke the returned unsubscribe callback to stop receiving updates. See
+ * {@link https://firebase.google.com/docs/database/web/retrieve-data | Retrieve Data on the Web}
+ * for more details.
+ *
+ * An `onChildChanged` event will be triggered when the data stored in a child
+ * (or any of its descendants) changes. Note that a single `child_changed` event
+ * may represent multiple changes to the child. The `DataSnapshot` passed to the
+ * callback will contain the new child contents. For ordering purposes, the
+ * callback is also passed a second argument which is a string containing the
+ * key of the previous sibling child by sort order, or `null` if it is the first
+ * child.
+ *
+ * @param query - The query to run.
+ * @param callback - A callback that fires when the specified event occurs.
+ * The callback will be passed a DataSnapshot and a string containing the key of
+ * the previous child, by sort order, or `null` if it is the first child.
+ * @param options - An object that can be used to configure `onlyOnce`, which
+ * then removes the listener after its first invocation.
+ * @returns A function that can be invoked to remove the listener.
+ */
+export declare function onChildChanged(query: Query, callback: (snapshot: DataSnapshot, previousChildName: string | null) => unknown, options: ListenOptions): Unsubscribe;
+/**
+ * Listens for data changes at a particular location.
+ *
+ * This is the primary way to read data from a Database. Your callback
+ * will be triggered for the initial data and again whenever the data changes.
+ * Invoke the returned unsubscribe callback to stop receiving updates. See
+ * {@link https://firebase.google.com/docs/database/web/retrieve-data | Retrieve Data on the Web}
+ * for more details.
+ *
+ * An `onChildChanged` event will be triggered when the data stored in a child
+ * (or any of its descendants) changes. Note that a single `child_changed` event
+ * may represent multiple changes to the child. The `DataSnapshot` passed to the
+ * callback will contain the new child contents. For ordering purposes, the
+ * callback is also passed a second argument which is a string containing the
+ * key of the previous sibling child by sort order, or `null` if it is the first
+ * child.
+ *
+ * @param query - The query to run.
+ * @param callback - A callback that fires when the specified event occurs.
+ * The callback will be passed a DataSnapshot and a string containing the key of
+ * the previous child, by sort order, or `null` if it is the first child.
+ * @param cancelCallback - An optional callback that will be notified if your
+ * event subscription is ever canceled because your client does not have
+ * permission to read this data (or it had permission but has now lost it).
+ * This callback will be passed an `Error` object indicating why the failure
+ * occurred.
+ * @param options - An object that can be used to configure `onlyOnce`, which
+ * then removes the listener after its first invocation.
+ * @returns A function that can be invoked to remove the listener.
+ */
+export declare function onChildChanged(query: Query, callback: (snapshot: DataSnapshot, previousChildName: string | null) => unknown, cancelCallback: (error: Error) => unknown, options: ListenOptions): Unsubscribe;
+/**
+ * Listens for data changes at a particular location.
+ *
+ * This is the primary way to read data from a Database. Your callback
+ * will be triggered for the initial data and again whenever the data changes.
+ * Invoke the returned unsubscribe callback to stop receiving updates. See
+ * {@link https://firebase.google.com/docs/database/web/retrieve-data | Retrieve Data on the Web}
+ * for more details.
+ *
+ * An `onChildMoved` event will be triggered when a child's sort order changes
+ * such that its position relative to its siblings changes. The `DataSnapshot`
+ * passed to the callback will be for the data of the child that has moved. It
+ * is also passed a second argument which is a string containing the key of the
+ * previous sibling child by sort order, or `null` if it is the first child.
+ *
+ * @param query - The query to run.
+ * @param callback - A callback that fires when the specified event occurs.
+ * The callback will be passed a DataSnapshot and a string containing the key of
+ * the previous child, by sort order, or `null` if it is the first child.
+ * @param cancelCallback - An optional callback that will be notified if your
+ * event subscription is ever canceled because your client does not have
+ * permission to read this data (or it had permission but has now lost it).
+ * This callback will be passed an `Error` object indicating why the failure
+ * occurred.
+ * @returns A function that can be invoked to remove the listener.
+ */
+export declare function onChildMoved(query: Query, callback: (snapshot: DataSnapshot, previousChildName: string | null) => unknown, cancelCallback?: (error: Error) => unknown): Unsubscribe;
+/**
+ * Listens for data changes at a particular location.
+ *
+ * This is the primary way to read data from a Database. Your callback
+ * will be triggered for the initial data and again whenever the data changes.
+ * Invoke the returned unsubscribe callback to stop receiving updates. See
+ * {@link https://firebase.google.com/docs/database/web/retrieve-data | Retrieve Data on the Web}
+ * for more details.
+ *
+ * An `onChildMoved` event will be triggered when a child's sort order changes
+ * such that its position relative to its siblings changes. The `DataSnapshot`
+ * passed to the callback will be for the data of the child that has moved. It
+ * is also passed a second argument which is a string containing the key of the
+ * previous sibling child by sort order, or `null` if it is the first child.
+ *
+ * @param query - The query to run.
+ * @param callback - A callback that fires when the specified event occurs.
+ * The callback will be passed a DataSnapshot and a string containing the key of
+ * the previous child, by sort order, or `null` if it is the first child.
+ * @param options - An object that can be used to configure `onlyOnce`, which
+ * then removes the listener after its first invocation.
+ * @returns A function that can be invoked to remove the listener.
+ */
+export declare function onChildMoved(query: Query, callback: (snapshot: DataSnapshot, previousChildName: string | null) => unknown, options: ListenOptions): Unsubscribe;
+/**
+ * Listens for data changes at a particular location.
+ *
+ * This is the primary way to read data from a Database. Your callback
+ * will be triggered for the initial data and again whenever the data changes.
+ * Invoke the returned unsubscribe callback to stop receiving updates. See
+ * {@link https://firebase.google.com/docs/database/web/retrieve-data | Retrieve Data on the Web}
+ * for more details.
+ *
+ * An `onChildMoved` event will be triggered when a child's sort order changes
+ * such that its position relative to its siblings changes. The `DataSnapshot`
+ * passed to the callback will be for the data of the child that has moved. It
+ * is also passed a second argument which is a string containing the key of the
+ * previous sibling child by sort order, or `null` if it is the first child.
+ *
+ * @param query - The query to run.
+ * @param callback - A callback that fires when the specified event occurs.
+ * The callback will be passed a DataSnapshot and a string containing the key of
+ * the previous child, by sort order, or `null` if it is the first child.
+ * @param cancelCallback - An optional callback that will be notified if your
+ * event subscription is ever canceled because your client does not have
+ * permission to read this data (or it had permission but has now lost it).
+ * This callback will be passed an `Error` object indicating why the failure
+ * occurred.
+ * @param options - An object that can be used to configure `onlyOnce`, which
+ * then removes the listener after its first invocation.
+ * @returns A function that can be invoked to remove the listener.
+ */
+export declare function onChildMoved(query: Query, callback: (snapshot: DataSnapshot, previousChildName: string | null) => unknown, cancelCallback: (error: Error) => unknown, options: ListenOptions): Unsubscribe;
+/**
+ * Listens for data changes at a particular location.
+ *
+ * This is the primary way to read data from a Database. Your callback
+ * will be triggered for the initial data and again whenever the data changes.
+ * Invoke the returned unsubscribe callback to stop receiving updates. See
+ * {@link https://firebase.google.com/docs/database/web/retrieve-data | Retrieve Data on the Web}
+ * for more details.
+ *
+ * An `onChildRemoved` event will be triggered once every time a child is
+ * removed. The `DataSnapshot` passed into the callback will be the old data for
+ * the child that was removed. A child will get removed when either:
+ *
+ * - a client explicitly calls `remove()` on that child or one of its ancestors
+ * - a client calls `set(null)` on that child or one of its ancestors
+ * - that child has all of its children removed
+ * - there is a query in effect which now filters out the child (because it's
+ *   sort order changed or the max limit was hit)
+ *
+ * @param query - The query to run.
+ * @param callback - A callback that fires when the specified event occurs.
+ * The callback will be passed a DataSnapshot and a string containing the key of
+ * the previous child, by sort order, or `null` if it is the first child.
+ * @param cancelCallback - An optional callback that will be notified if your
+ * event subscription is ever canceled because your client does not have
+ * permission to read this data (or it had permission but has now lost it).
+ * This callback will be passed an `Error` object indicating why the failure
+ * occurred.
+ * @returns A function that can be invoked to remove the listener.
+ */
+export declare function onChildRemoved(query: Query, callback: (snapshot: DataSnapshot) => unknown, cancelCallback?: (error: Error) => unknown): Unsubscribe;
+/**
+ * Listens for data changes at a particular location.
+ *
+ * This is the primary way to read data from a Database. Your callback
+ * will be triggered for the initial data and again whenever the data changes.
+ * Invoke the returned unsubscribe callback to stop receiving updates. See
+ * {@link https://firebase.google.com/docs/database/web/retrieve-data | Retrieve Data on the Web}
+ * for more details.
+ *
+ * An `onChildRemoved` event will be triggered once every time a child is
+ * removed. The `DataSnapshot` passed into the callback will be the old data for
+ * the child that was removed. A child will get removed when either:
+ *
+ * - a client explicitly calls `remove()` on that child or one of its ancestors
+ * - a client calls `set(null)` on that child or one of its ancestors
+ * - that child has all of its children removed
+ * - there is a query in effect which now filters out the child (because it's
+ *   sort order changed or the max limit was hit)
+ *
+ * @param query - The query to run.
+ * @param callback - A callback that fires when the specified event occurs.
+ * The callback will be passed a DataSnapshot and a string containing the key of
+ * the previous child, by sort order, or `null` if it is the first child.
+ * @param options - An object that can be used to configure `onlyOnce`, which
+ * then removes the listener after its first invocation.
+ * @returns A function that can be invoked to remove the listener.
+ */
+export declare function onChildRemoved(query: Query, callback: (snapshot: DataSnapshot) => unknown, options: ListenOptions): Unsubscribe;
+/**
+ * Listens for data changes at a particular location.
+ *
+ * This is the primary way to read data from a Database. Your callback
+ * will be triggered for the initial data and again whenever the data changes.
+ * Invoke the returned unsubscribe callback to stop receiving updates. See
+ * {@link https://firebase.google.com/docs/database/web/retrieve-data | Retrieve Data on the Web}
+ * for more details.
+ *
+ * An `onChildRemoved` event will be triggered once every time a child is
+ * removed. The `DataSnapshot` passed into the callback will be the old data for
+ * the child that was removed. A child will get removed when either:
+ *
+ * - a client explicitly calls `remove()` on that child or one of its ancestors
+ * - a client calls `set(null)` on that child or one of its ancestors
+ * - that child has all of its children removed
+ * - there is a query in effect which now filters out the child (because it's
+ *   sort order changed or the max limit was hit)
+ *
+ * @param query - The query to run.
+ * @param callback - A callback that fires when the specified event occurs.
+ * The callback will be passed a DataSnapshot and a string containing the key of
+ * the previous child, by sort order, or `null` if it is the first child.
+ * @param cancelCallback - An optional callback that will be notified if your
+ * event subscription is ever canceled because your client does not have
+ * permission to read this data (or it had permission but has now lost it).
+ * This callback will be passed an `Error` object indicating why the failure
+ * occurred.
+ * @param options - An object that can be used to configure `onlyOnce`, which
+ * then removes the listener after its first invocation.
+ * @returns A function that can be invoked to remove the listener.
+ */
+export declare function onChildRemoved(query: Query, callback: (snapshot: DataSnapshot) => unknown, cancelCallback: (error: Error) => unknown, options: ListenOptions): Unsubscribe;
+/**
+ * The `onDisconnect` class allows you to write or clear data when your client
+ * disconnects from the Database server. These updates occur whether your
+ * client disconnects cleanly or not, so you can rely on them to clean up data
+ * even if a connection is dropped or a client crashes.
+ *
+ * The `onDisconnect` class is most commonly used to manage presence in
+ * applications where it is useful to detect how many clients are connected and
+ * when other clients disconnect. See
+ * {@link https://firebase.google.com/docs/database/web/offline-capabilities | Enabling Offline Capabilities in JavaScript}
+ * for more information.
+ *
+ * To avoid problems when a connection is dropped before the requests can be
+ * transferred to the Database server, these functions should be called before
+ * writing any data.
+ *
+ * Note that `onDisconnect` operations are only triggered once. If you want an
+ * operation to occur each time a disconnect occurs, you'll need to re-establish
+ * the `onDisconnect` operations each time you reconnect.
+ */
+export declare class OnDisconnect {
+    private constructor();
+    /**
+     * Cancels all previously queued `onDisconnect()` set or update events for this
+     * location and all children.
+     *
+     * If a write has been queued for this location via a `set()` or `update()` at a
+     * parent location, the write at this location will be canceled, though writes
+     * to sibling locations will still occur.
+     *
+     * @returns Resolves when synchronization to the server is complete.
+     */
+    cancel(): Promise<void>;
+    /**
+     * Ensures the data at this location is deleted when the client is disconnected
+     * (due to closing the browser, navigating to a new page, or network issues).
+     *
+     * @returns Resolves when synchronization to the server is complete.
+     */
+    remove(): Promise<void>;
+    /**
+     * Ensures the data at this location is set to the specified value when the
+     * client is disconnected (due to closing the browser, navigating to a new page,
+     * or network issues).
+     *
+     * `set()` is especially useful for implementing "presence" systems, where a
+     * value should be changed or cleared when a user disconnects so that they
+     * appear "offline" to other users. See
+     * {@link https://firebase.google.com/docs/database/web/offline-capabilities | Enabling Offline Capabilities in JavaScript}
+     * for more information.
+     *
+     * Note that `onDisconnect` operations are only triggered once. If you want an
+     * operation to occur each time a disconnect occurs, you'll need to re-establish
+     * the `onDisconnect` operations each time.
+     *
+     * @param value - The value to be written to this location on disconnect (can
+     * be an object, array, string, number, boolean, or null).
+     * @returns Resolves when synchronization to the Database is complete.
+     */
+    set(value: unknown): Promise<void>;
+    /**
+     * Ensures the data at this location is set to the specified value and priority
+     * when the client is disconnected (due to closing the browser, navigating to a
+     * new page, or network issues).
+     *
+     * @param value - The value to be written to this location on disconnect (can
+     * be an object, array, string, number, boolean, or null).
+     * @param priority - The priority to be written (string, number, or null).
+     * @returns Resolves when synchronization to the Database is complete.
+     */
+    setWithPriority(value: unknown, priority: number | string | null): Promise<void>;
+    /**
+     * Writes multiple values at this location when the client is disconnected (due
+     * to closing the browser, navigating to a new page, or network issues).
+     *
+     * The `values` argument contains multiple property-value pairs that will be
+     * written to the Database together. Each child property can either be a simple
+     * property (for example, "name") or a relative path (for example, "name/first")
+     * from the current location to the data to update.
+     *
+     * As opposed to the `set()` method, `update()` can be use to selectively update
+     * only the referenced properties at the current location (instead of replacing
+     * all the child properties at the current location).
+     *
+     * @param values - Object containing multiple values.
+     * @returns Resolves when synchronization to the Database is complete.
+     */
+    update(values: object): Promise<void>;
+}
+/**
+ * Returns an `OnDisconnect` object - see
+ * {@link https://firebase.google.com/docs/database/web/offline-capabilities | Enabling Offline Capabilities in JavaScript}
+ * for more information on how to use it.
+ *
+ * @param ref - The reference to add OnDisconnect triggers for.
+ */
+export declare function onDisconnect(ref: DatabaseReference): OnDisconnect;
+/**
+ * Listens for data changes at a particular location.
+ *
+ * This is the primary way to read data from a Database. Your callback
+ * will be triggered for the initial data and again whenever the data changes.
+ * Invoke the returned unsubscribe callback to stop receiving updates. See
+ * {@link https://firebase.google.com/docs/database/web/retrieve-data | Retrieve Data on the Web}
+ * for more details.
+ *
+ * An `onValue` event will trigger once with the initial data stored at this
+ * location, and then trigger again each time the data changes. The
+ * `DataSnapshot` passed to the callback will be for the location at which
+ * `on()` was called. It won't trigger until the entire contents has been
+ * synchronized. If the location has no data, it will be triggered with an empty
+ * `DataSnapshot` (`val()` will return `null`).
+ *
+ * @param query - The query to run.
+ * @param callback - A callback that fires when the specified event occurs. The
+ * callback will be passed a DataSnapshot.
+ * @param cancelCallback - An optional callback that will be notified if your
+ * event subscription is ever canceled because your client does not have
+ * permission to read this data (or it had permission but has now lost it).
+ * This callback will be passed an `Error` object indicating why the failure
+ * occurred.
+ * @returns A function that can be invoked to remove the listener.
+ */
+export declare function onValue(query: Query, callback: (snapshot: DataSnapshot) => unknown, cancelCallback?: (error: Error) => unknown): Unsubscribe;
+/**
+ * Listens for data changes at a particular location.
+ *
+ * This is the primary way to read data from a Database. Your callback
+ * will be triggered for the initial data and again whenever the data changes.
+ * Invoke the returned unsubscribe callback to stop receiving updates. See
+ * {@link https://firebase.google.com/docs/database/web/retrieve-data | Retrieve Data on the Web}
+ * for more details.
+ *
+ * An `onValue` event will trigger once with the initial data stored at this
+ * location, and then trigger again each time the data changes. The
+ * `DataSnapshot` passed to the callback will be for the location at which
+ * `on()` was called. It won't trigger until the entire contents has been
+ * synchronized. If the location has no data, it will be triggered with an empty
+ * `DataSnapshot` (`val()` will return `null`).
+ *
+ * @param query - The query to run.
+ * @param callback - A callback that fires when the specified event occurs. The
+ * callback will be passed a DataSnapshot.
+ * @param options - An object that can be used to configure `onlyOnce`, which
+ * then removes the listener after its first invocation.
+ * @returns A function that can be invoked to remove the listener.
+ */
+export declare function onValue(query: Query, callback: (snapshot: DataSnapshot) => unknown, options: ListenOptions): Unsubscribe;
+/**
+ * Listens for data changes at a particular location.
+ *
+ * This is the primary way to read data from a Database. Your callback
+ * will be triggered for the initial data and again whenever the data changes.
+ * Invoke the returned unsubscribe callback to stop receiving updates. See
+ * {@link https://firebase.google.com/docs/database/web/retrieve-data | Retrieve Data on the Web}
+ * for more details.
+ *
+ * An `onValue` event will trigger once with the initial data stored at this
+ * location, and then trigger again each time the data changes. The
+ * `DataSnapshot` passed to the callback will be for the location at which
+ * `on()` was called. It won't trigger until the entire contents has been
+ * synchronized. If the location has no data, it will be triggered with an empty
+ * `DataSnapshot` (`val()` will return `null`).
+ *
+ * @param query - The query to run.
+ * @param callback - A callback that fires when the specified event occurs. The
+ * callback will be passed a DataSnapshot.
+ * @param cancelCallback - An optional callback that will be notified if your
+ * event subscription is ever canceled because your client does not have
+ * permission to read this data (or it had permission but has now lost it).
+ * This callback will be passed an `Error` object indicating why the failure
+ * occurred.
+ * @param options - An object that can be used to configure `onlyOnce`, which
+ * then removes the listener after its first invocation.
+ * @returns A function that can be invoked to remove the listener.
+ */
+export declare function onValue(query: Query, callback: (snapshot: DataSnapshot) => unknown, cancelCallback: (error: Error) => unknown, options: ListenOptions): Unsubscribe;
+/**
+ * Creates a new `QueryConstraint` that orders by the specified child key.
+ *
+ * Queries can only order by one key at a time. Calling `orderByChild()`
+ * multiple times on the same query is an error.
+ *
+ * Firebase queries allow you to order your data by any child key on the fly.
+ * However, if you know in advance what your indexes will be, you can define
+ * them via the .indexOn rule in your Security Rules for better performance. See
+ * the{@link https://firebase.google.com/docs/database/security/indexing-data}
+ * rule for more information.
+ *
+ * You can read more about `orderByChild()` in
+ * {@link https://firebase.google.com/docs/database/web/lists-of-data#sort_data | Sort data}.
+ *
+ * @param path - The path to order by.
+ */
+export declare function orderByChild(path: string): QueryConstraint;
+/**
+ * Creates a new `QueryConstraint` that orders by the key.
+ *
+ * Sorts the results of a query by their (ascending) key values.
+ *
+ * You can read more about `orderByKey()` in
+ * {@link https://firebase.google.com/docs/database/web/lists-of-data#sort_data | Sort data}.
+ */
+export declare function orderByKey(): QueryConstraint;
+/**
+ * Creates a new `QueryConstraint` that orders by priority.
+ *
+ * Applications need not use priority but can order collections by
+ * ordinary properties (see
+ * {@link https://firebase.google.com/docs/database/web/lists-of-data#sort_data | Sort data}
+ * for alternatives to priority.
+ */
+export declare function orderByPriority(): QueryConstraint;
+/**
+ * Creates a new `QueryConstraint` that orders by value.
+ *
+ * If the children of a query are all scalar values (string, number, or
+ * boolean), you can order the results by their (ascending) values.
+ *
+ * You can read more about `orderByValue()` in
+ * {@link https://firebase.google.com/docs/database/web/lists-of-data#sort_data | Sort data}.
+ */
+export declare function orderByValue(): QueryConstraint;
+/**
+ * Generates a new child location using a unique key and returns its
+ * `Reference`.
+ *
+ * This is the most common pattern for adding data to a collection of items.
+ *
+ * If you provide a value to `push()`, the value is written to the
+ * generated location. If you don't pass a value, nothing is written to the
+ * database and the child remains empty (but you can use the `Reference`
+ * elsewhere).
+ *
+ * The unique keys generated by `push()` are ordered by the current time, so the
+ * resulting list of items is chronologically sorted. The keys are also
+ * designed to be unguessable (they contain 72 random bits of entropy).
+ *
+ * See {@link https://firebase.google.com/docs/database/web/lists-of-data#append_to_a_list_of_data | Append to a list of data}.
+ * See {@link https://firebase.googleblog.com/2015/02/the-2120-ways-to-ensure-unique_68.html | The 2^120 Ways to Ensure Unique Identifiers}.
+ *
+ * @param parent - The parent location.
+ * @param value - Optional value to be written at the generated location.
+ * @returns Combined `Promise` and `Reference`; resolves when write is complete,
+ * but can be used immediately as the `Reference` to the child location.
+ */
+export declare function push(parent: DatabaseReference, value?: unknown): ThenableReference;
+/**
+ * @license
+ * Copyright 2021 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+/**
+ * A `Query` sorts and filters the data at a Database location so only a subset
+ * of the child data is included. This can be used to order a collection of
+ * data by some attribute (for example, height of dinosaurs) as well as to
+ * restrict a large list of items (for example, chat messages) down to a number
+ * suitable for synchronizing to the client. Queries are created by chaining
+ * together one or more of the filter methods defined here.
+ *
+ * Just as with a `DatabaseReference`, you can receive data from a `Query` by using the
+ * `on*()` methods. You will only receive events and `DataSnapshot`s for the
+ * subset of the data that matches your query.
+ *
+ * See {@link https://firebase.google.com/docs/database/web/lists-of-data#sorting_and_filtering_data}
+ * for more information.
+ */
+export declare interface Query {
+    /** The `DatabaseReference` for the `Query`'s location. */
+    readonly ref: DatabaseReference;
+    /**
+     * Returns whether or not the current and provided queries represent the same
+     * location, have the same query parameters, and are from the same instance of
+     * `FirebaseApp`.
+     *
+     * Two `DatabaseReference` objects are equivalent if they represent the same location
+     * and are from the same instance of `FirebaseApp`.
+     *
+     * Two `Query` objects are equivalent if they represent the same location,
+     * have the same query parameters, and are from the same instance of
+     * `FirebaseApp`. Equivalent queries share the same sort order, limits, and
+     * starting and ending points.
+     *
+     * @param other - The query to compare against.
+     * @returns Whether or not the current and provided queries are equivalent.
+     */
+    isEqual(other: Query | null): boolean;
+    /**
+     * Returns a JSON-serializable representation of this object.
+     *
+     * @returns A JSON-serializable representation of this object.
+     */
+    toJSON(): string;
+    /**
+     * Gets the absolute URL for this location.
+     *
+     * The `toString()` method returns a URL that is ready to be put into a
+     * browser, curl command, or a `refFromURL()` call. Since all of those expect
+     * the URL to be url-encoded, `toString()` returns an encoded URL.
+     *
+     * Append '.json' to the returned URL when typed into a browser to download
+     * JSON-formatted data. If the location is secured (that is, not publicly
+     * readable), you will get a permission-denied error.
+     *
+     * @returns The absolute URL for this location.
+     */
+    toString(): string;
+}
+/**
+ * Creates a new immutable instance of `Query` that is extended to also include
+ * additional query constraints.
+ *
+ * @param query - The Query instance to use as a base for the new constraints.
+ * @param queryConstraints - The list of `QueryConstraint`s to apply.
+ * @throws if any of the provided query constraints cannot be combined with the
+ * existing or new constraints.
+ */
+export declare function query(query: Query, ...queryConstraints: QueryConstraint[]): Query;
+/**
+ * A `QueryConstraint` is used to narrow the set of documents returned by a
+ * Database query. `QueryConstraint`s are created by invoking {@link endAt},
+ * {@link endBefore}, {@link startAt}, {@link startAfter}, {@link
+ * limitToFirst}, {@link limitToLast}, {@link orderByChild},
+ * {@link orderByChild}, {@link orderByKey} , {@link orderByPriority} ,
+ * {@link orderByValue}  or {@link equalTo} and
+ * can then be passed to {@link query} to create a new query instance that
+ * also contains this `QueryConstraint`.
+ */
+export declare abstract class QueryConstraint {
+    /** The type of this query constraints */
+    abstract readonly type: QueryConstraintType;
+}
+/** Describes the different query constraints available in this SDK. */
+export declare type QueryConstraintType = 'endAt' | 'endBefore' | 'startAt' | 'startAfter' | 'limitToFirst' | 'limitToLast' | 'orderByChild' | 'orderByKey' | 'orderByPriority' | 'orderByValue' | 'equalTo';
+/* Excluded from this release type: _QueryImpl */
+/* Excluded from this release type: _QueryParams */
+/**
+ *
+ * Returns a `Reference` representing the location in the Database
+ * corresponding to the provided path. If no path is provided, the `Reference`
+ * will point to the root of the Database.
+ *
+ * @param db - The database instance to obtain a reference for.
+ * @param path - Optional path representing the location the returned
+ *   `Reference` will point. If not provided, the returned `Reference` will
+ *   point to the root of the Database.
+ * @returns If a path is provided, a `Reference`
+ *   pointing to the provided path. Otherwise, a `Reference` pointing to the
+ *   root of the Database.
+ */
+export declare function ref(db: Database, path?: string): DatabaseReference;
+/* Excluded from this release type: _ReferenceImpl */
+/**
+ * Returns a `Reference` representing the location in the Database
+ * corresponding to the provided Firebase URL.
+ *
+ * An exception is thrown if the URL is not a valid Firebase Database URL or it
+ * has a different domain than the current `Database` instance.
+ *
+ * Note that all query parameters (`orderBy`, `limitToLast`, etc.) are ignored
+ * and are not applied to the returned `Reference`.
+ *
+ * @param db - The database instance to obtain a reference for.
+ * @param url - The Firebase URL at which the returned `Reference` will
+ *   point.
+ * @returns A `Reference` pointing to the provided
+ *   Firebase URL.
+ */
+export declare function refFromURL(db: Database, url: string): DatabaseReference;
+/**
+ * Removes the data at this Database location.
+ *
+ * Any data at child locations will also be deleted.
+ *
+ * The effect of the remove will be visible immediately and the corresponding
+ * event 'value' will be triggered. Synchronization of the remove to the
+ * Firebase servers will also be started, and the returned Promise will resolve
+ * when complete. If provided, the onComplete callback will be called
+ * asynchronously after synchronization has finished.
+ *
+ * @param ref - The location to remove.
+ * @returns Resolves when remove on server is complete.
+ */
+export declare function remove(ref: DatabaseReference): Promise<void>;
+/* Excluded from this release type: _repoManagerDatabaseFromApp */
+/**
+ * Atomically modifies the data at this location.
+ *
+ * Atomically modify the data at this location. Unlike a normal `set()`, which
+ * just overwrites the data regardless of its previous value, `runTransaction()` is
+ * used to modify the existing value to a new value, ensuring there are no
+ * conflicts with other clients writing to the same location at the same time.
+ *
+ * To accomplish this, you pass `runTransaction()` an update function which is
+ * used to transform the current value into a new value. If another client
+ * writes to the location before your new value is successfully written, your
+ * update function will be called again with the new current value, and the
+ * write will be retried. This will happen repeatedly until your write succeeds
+ * without conflict or you abort the transaction by not returning a value from
+ * your update function.
+ *
+ * Note: Modifying data with `set()` will cancel any pending transactions at
+ * that location, so extreme care should be taken if mixing `set()` and
+ * `runTransaction()` to update the same data.
+ *
+ * Note: When using transactions with Security and Firebase Rules in place, be
+ * aware that a client needs `.read` access in addition to `.write` access in
+ * order to perform a transaction. This is because the client-side nature of
+ * transactions requires the client to read the data in order to transactionally
+ * update it.
+ *
+ * @param ref - The location to atomically modify.
+ * @param transactionUpdate - A developer-supplied function which will be passed
+ * the current data stored at this location (as a JavaScript object). The
+ * function should return the new value it would like written (as a JavaScript
+ * object). If `undefined` is returned (i.e. you return with no arguments) the
+ * transaction will be aborted and the data at this location will not be
+ * modified.
+ * @param options - An options object to configure transactions.
+ * @returns A `Promise` that can optionally be used instead of the `onComplete`
+ * callback to handle success and failure.
+ */
+export declare function runTransaction(ref: DatabaseReference, transactionUpdate: (currentData: any) => unknown, options?: TransactionOptions): Promise<TransactionResult>;
+/**
+ * @license
+ * Copyright 2020 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+/**
+ * Returns a placeholder value for auto-populating the current timestamp (time
+ * since the Unix epoch, in milliseconds) as determined by the Firebase
+ * servers.
+ */
+export declare function serverTimestamp(): object;
+/**
+ * Writes data to this Database location.
+ *
+ * This will overwrite any data at this location and all child locations.
+ *
+ * The effect of the write will be visible immediately, and the corresponding
+ * events ("value", "child_added", etc.) will be triggered. Synchronization of
+ * the data to the Firebase servers will also be started, and the returned
+ * Promise will resolve when complete. If provided, the `onComplete` callback
+ * will be called asynchronously after synchronization has finished.
+ *
+ * Passing `null` for the new value is equivalent to calling `remove()`; namely,
+ * all data at this location and all child locations will be deleted.
+ *
+ * `set()` will remove any priority stored at this location, so if priority is
+ * meant to be preserved, you need to use `setWithPriority()` instead.
+ *
+ * Note that modifying data with `set()` will cancel any pending transactions
+ * at that location, so extreme care should be taken if mixing `set()` and
+ * `transaction()` to modify the same data.
+ *
+ * A single `set()` will generate a single "value" event at the location where
+ * the `set()` was performed.
+ *
+ * @param ref - The location to write to.
+ * @param value - The value to be written (string, number, boolean, object,
+ *   array, or null).
+ * @returns Resolves when write to server is complete.
+ */
+export declare function set(ref: DatabaseReference, value: unknown): Promise<void>;
+/**
+ * Sets a priority for the data at this Database location.
+ *
+ * Applications need not use priority but can order collections by
+ * ordinary properties (see
+ * {@link https://firebase.google.com/docs/database/web/lists-of-data#sorting_and_filtering_data | Sorting and filtering data}
+ * ).
+ *
+ * @param ref - The location to write to.
+ * @param priority - The priority to be written (string, number, or null).
+ * @returns Resolves when write to server is complete.
+ */
+export declare function setPriority(ref: DatabaseReference, priority: string | number | null): Promise<void>;
+/* Excluded from this release type: _setSDKVersion */
+/**
+ * Writes data the Database location. Like `set()` but also specifies the
+ * priority for that data.
+ *
+ * Applications need not use priority but can order collections by
+ * ordinary properties (see
+ * {@link https://firebase.google.com/docs/database/web/lists-of-data#sorting_and_filtering_data | Sorting and filtering data}
+ * ).
+ *
+ * @param ref - The location to write to.
+ * @param value - The value to be written (string, number, boolean, object,
+ *   array, or null).
+ * @param priority - The priority to be written (string, number, or null).
+ * @returns Resolves when write to server is complete.
+ */
+export declare function setWithPriority(ref: DatabaseReference, value: unknown, priority: string | number | null): Promise<void>;
+/**
+ * Creates a `QueryConstraint` with the specified starting point (exclusive).
+ *
+ * Using `startAt()`, `startAfter()`, `endBefore()`, `endAt()` and `equalTo()`
+ * allows you to choose arbitrary starting and ending points for your queries.
+ *
+ * The starting point is exclusive. If only a value is provided, children
+ * with a value greater than the specified value will be included in the query.
+ * If a key is specified, then children must have a value greater than or equal
+ * to the specified value and a a key name greater than the specified key.
+ *
+ * @param value - The value to start after. The argument type depends on which
+ * `orderBy*()` function was used in this query. Specify a value that matches
+ * the `orderBy*()` type. When used in combination with `orderByKey()`, the
+ * value must be a string.
+ * @param key - The child key to start after. This argument is only allowed if
+ * ordering by child, value, or priority.
+ */
+export declare function startAfter(value: number | string | boolean | null, key?: string): QueryConstraint;
+/**
+ * Creates a `QueryConstraint` with the specified starting point.
+ *
+ * Using `startAt()`, `startAfter()`, `endBefore()`, `endAt()` and `equalTo()`
+ * allows you to choose arbitrary starting and ending points for your queries.
+ *
+ * The starting point is inclusive, so children with exactly the specified value
+ * will be included in the query. The optional key argument can be used to
+ * further limit the range of the query. If it is specified, then children that
+ * have exactly the specified value must also have a key name greater than or
+ * equal to the specified key.
+ *
+ * You can read more about `startAt()` in
+ * {@link https://firebase.google.com/docs/database/web/lists-of-data#filtering_data | Filtering data}.
+ *
+ * @param value - The value to start at. The argument type depends on which
+ * `orderBy*()` function was used in this query. Specify a value that matches
+ * the `orderBy*()` type. When used in combination with `orderByKey()`, the
+ * value must be a string.
+ * @param key - The child key to start at. This argument is only allowed if
+ * ordering by child, value, or priority.
+ */
+export declare function startAt(value?: number | string | boolean | null, key?: string): QueryConstraint;
+/* Excluded from this release type: _TEST_ACCESS_forceRestClient */
+/* Excluded from this release type: _TEST_ACCESS_hijackHash */
+/**
+ * A `Promise` that can also act as a `DatabaseReference` when returned by
+ * {@link push}. The reference is available immediately and the `Promise` resolves
+ * as the write to the backend completes.
+ */
+export declare interface ThenableReference extends DatabaseReference, Pick<Promise<DatabaseReference>, 'then' | 'catch'> {
+    key: string;
+    parent: DatabaseReference;
+}
+/** An options object to configure transactions. */
+export declare interface TransactionOptions {
+    /**
+     * By default, events are raised each time the transaction update function
+     * runs. So if it is run multiple times, you may see intermediate states. You
+     * can set this to false to suppress these intermediate states and instead
+     * wait until the transaction has completed before events are raised.
+     */
+    readonly applyLocally?: boolean;
+}
+/**
+ * A type for the resolve value of {@link runTransaction}.
+ */
+export declare class TransactionResult {
+    /** Whether the transaction was successfully committed. */
+    readonly committed: boolean;
+    /** The resulting data snapshot. */
+    readonly snapshot: DataSnapshot;
+    private constructor();
+    /** Returns a JSON-serializable representation of this object. */
+    toJSON(): object;
+}
+/** A callback that can invoked to remove a listener. */
+export declare type Unsubscribe = () => void;
+/**
+ * Writes multiple values to the Database at once.
+ *
+ * The `values` argument contains multiple property-value pairs that will be
+ * written to the Database together. Each child property can either be a simple
+ * property (for example, "name") or a relative path (for example,
+ * "name/first") from the current location to the data to update.
+ *
+ * As opposed to the `set()` method, `update()` can be use to selectively update
+ * only the referenced properties at the current location (instead of replacing
+ * all the child properties at the current location).
+ *
+ * The effect of the write will be visible immediately, and the corresponding
+ * events ('value', 'child_added', etc.) will be triggered. Synchronization of
+ * the data to the Firebase servers will also be started, and the returned
+ * Promise will resolve when complete. If provided, the `onComplete` callback
+ * will be called asynchronously after synchronization has finished.
+ *
+ * A single `update()` will generate a single "value" event at the location
+ * where the `update()` was performed, regardless of how many children were
+ * modified.
+ *
+ * Note that modifying data with `update()` will cancel any pending
+ * transactions at that location, so extreme care should be taken if mixing
+ * `update()` and `transaction()` to modify the same data.
+ *
+ * Passing `null` to `update()` will remove the data at this location.
+ *
+ * See
+ * {@link https://firebase.googleblog.com/2015/09/introducing-multi-location-updates-and_86.html | Introducing multi-location updates and more}.
+ *
+ * @param ref - The location to write to.
+ * @param values - Object containing multiple values.
+ * @returns Resolves when update on server is complete.
+ */
+export declare function update(ref: DatabaseReference, values: object): Promise<void>;
+export {};