A Reference 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 firebase.database().ref() or firebase.database().ref("child/path").

Writing is done with the set() method and reading can be done with the on() method. See Read and Write Data on the Web

Index

Properties

Methods

Properties

key

key: string | null

The last part of the Reference's path.

For example, "ada" is the key for https://<DATABASE_NAME>.firebaseio.com/users/ada.

The key of a root Reference is null.

example
// The key of a root reference is null
var rootRef = firebase.database().ref();
var key = rootRef.key;  // key === null
example
// The key of any non-root reference is the last token in the path
var adaRef = firebase.database().ref("users/ada");
var key = adaRef.key;  // key === "ada"
key = adaRef.child("name/last").key;  // key === "last"

parent

parent: Reference | null

The parent location of a Reference.

The parent of a root Reference is null.

example
// The parent of a root reference is null
var rootRef = firebase.database().ref();
parent = rootRef.parent;  // parent === null
example
// The parent of any non-root reference is the parent location
var usersRef = firebase.database().ref("users");
var adaRef = firebase.database().ref("users/ada");
// usersRef and adaRef.parent represent the same location

ref

ref: Reference

Returns a Reference to the Query's location.

root

root: Reference

The root Reference of the Database.

example
// The root of a root reference is itself
var rootRef = firebase.database().ref();
// rootRef and rootRef.root represent the same location
example
// The root of any non-root reference is the root location
var adaRef = firebase.database().ref("users/ada");
// rootRef and adaRef.root represent the same location

Methods

child

  • child ( path :  string ) : Reference

  • 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").

    example
    var usersRef = firebase.database().ref('users');
var adaRef = usersRef.child('ada');
var adaFirstNameRef = adaRef.child('name/first');
var path = adaFirstNameRef.toString();
// path is now 'https://sample-app.firebaseio.com/users/ada/name/first'

    Parameters

    • path: string

      A relative path from this location to the desired child location.

    Returns Reference

    The specified child location.

endAt

  • endAt ( value :  number | string | boolean | null ,  key ? :  string ) : Query

  • Creates a Query 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 Filtering data.

    example
    // Find all dinosaurs whose names come before Pterodactyl lexicographically.
// Include Pterodactyl in the result.
var ref = firebase.database().ref("dinosaurs");
ref.orderByKey().endAt("pterodactyl").on("child_added", function(snapshot) {
  console.log(snapshot.key);
});

    Parameters

    • value: number | string | boolean | null

      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.

    • Optional key: string

      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.

    Returns Query

endBefore

  • endBefore ( value :  number | string | boolean | null ,  key ? :  string ) : Query

  • Creates a Query 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 lesss than or equal to the specified value and a a key name less than the specified key.

    example
    // Find all dinosaurs whose names come before Pterodactyl lexicographically.
// Do not include Pterodactyl in the result.
var ref = firebase.database().ref("dinosaurs");
ref.orderByKey().endBefore("pterodactyl").on("child_added", function(snapshot) {
  console.log(snapshot.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.

    Parameters

    • value: number | string | boolean | null
    • Optional key: string

    Returns Query

equalTo

  • equalTo ( value :  number | string | boolean | null ,  key ? :  string ) : Query

  • Creates a Query 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 Filtering data.

    example
    // Find all dinosaurs whose height is exactly 25 meters.
var ref = firebase.database().ref("dinosaurs");
ref.orderByChild("height").equalTo(25).on("child_added", function(snapshot) {
  console.log(snapshot.key);
});

    Parameters

    • value: number | string | boolean | null

      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.

    • Optional key: string

      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.

    Returns Query

get

  • get ( ) : Promise < DataSnapshot >

  • Gets the most up-to-date result for this query.

    Returns Promise<DataSnapshot>

    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).

isEqual

  • isEqual ( other :  Query | null ) : boolean

  • 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 firebase.app.App.

    Two Reference objects are equivalent if they represent the same location and are from the same instance of firebase.app.App.

    Two Query objects are equivalent if they represent the same location, have the same query parameters, and are from the same instance of firebase.app.App. Equivalent queries share the same sort order, limits, and starting and ending points.

    example
    var rootRef = firebase.database.ref();
var usersRef = rootRef.child("users");

usersRef.isEqual(rootRef);  // false
usersRef.isEqual(rootRef.child("users"));  // true
usersRef.parent.isEqual(rootRef);  // true
    example
    var rootRef = firebase.database.ref();
var usersRef = rootRef.child("users");
var usersQuery = usersRef.limitToLast(10);

usersQuery.isEqual(usersRef);  // false
usersQuery.isEqual(usersRef.limitToLast(10));  // true
usersQuery.isEqual(rootRef.limitToLast(10));  // false
usersQuery.isEqual(usersRef.orderByKey().limitToLast(10));  // false

    Parameters

    • other: Query | null

      The query to compare against.

    Returns boolean

    Whether or not the current and provided queries are equivalent.

limitToFirst

  • limitToFirst ( limit :  number ) : Query

  • Generates a new Query 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 Filtering data.

    example
    // Find the two shortest dinosaurs.
var ref = firebase.database().ref("dinosaurs");
ref.orderByChild("height").limitToFirst(2).on("child_added", function(snapshot) {
  // This will be called exactly two times (unless there are less than two
  // dinosaurs in the Database).

  // It will also get fired again if one of the first two dinosaurs is
  // removed from the data set, as a new dinosaur will now be the second
  // shortest.
  console.log(snapshot.key);
});

    Parameters

    • limit: number

      The maximum number of nodes to include in this query.

    Returns Query

limitToLast

  • limitToLast ( limit :  number ) : Query

  • Generates a new Query object limited to the last specific 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 Filtering data.

    example
    // Find the two heaviest dinosaurs.
var ref = firebase.database().ref("dinosaurs");
ref.orderByChild("weight").limitToLast(2).on("child_added", function(snapshot) {
  // This callback will be triggered exactly two times, unless there are
  // fewer than two dinosaurs stored in the Database. It will also get fired
  // for every new, heavier dinosaur that gets added to the data set.
  console.log(snapshot.key);
});

    Parameters

    • limit: number

      The maximum number of nodes to include in this query.

    Returns Query

off

  • off ( eventType ? :  EventType ,  callback ? :  ( a :  DataSnapshot ,  b ? :  string | null ) => any ,  context ? :  Object | null ) : void

  • Detaches a callback previously attached with on().

    Detach a callback previously attached with on(). Note that if on() was called multiple times with the same eventType and callback, the callback will be called multiple times for each event, and off() must be called multiple times to remove the callback. 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.

    example
    var onValueChange = function(dataSnapshot) {  ... };
ref.on('value', onValueChange);
ref.child('meta-data').on('child_added', onChildAdded);
// Sometime later...
ref.off('value', onValueChange);

// You must also call off() for any child listeners on ref
// to cancel those callbacks
ref.child('meta-data').off('child_added', onValueAdded);
    example
    // Or you can save a line of code by using an inline function
// and on()'s return value.
var onValueChange = ref.on('value', function(dataSnapshot) { ... });
// Sometime later...
ref.off('value', onValueChange);

    Parameters

    • Optional eventType: 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.

    • Optional callback: (a: DataSnapshot, b?: string | null) => any

      The callback function that was passed to on() or undefined to remove all callbacks.

    • Optional context: Object | null

      The context that was passed to on().

    Returns void

on

  • on ( eventType :  EventType ,  callback :  ( a :  DataSnapshot ,  b ? :  string | null ) => any ,  cancelCallbackOrContext ? :  ( ( a :  Error ) => any ) | Object | null ,  context ? :  Object | null ) : ( a :  DataSnapshot | null ,  b ? :  string | null ) => any

  • 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. Use off( ) to stop receiving updates. See Retrieve Data on the Web for more details.

    value event

    This 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).

    child_added event

    This 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.

    child_removed event

    This 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)

    child_changed event

    This 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.

    child_moved event

    This 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.

    example

    Handle a new value:

    ref.on('value', function(dataSnapshot) {
  ...
});
    example

    Handle a new child:

    ref.on('child_added', function(childSnapshot, prevChildKey) {
  ...
});
    example

    Handle child removal:

    ref.on('child_removed', function(oldChildSnapshot) {
  ...
});
    example

    Handle child data changes:

    ref.on('child_changed', function(childSnapshot, prevChildKey) {
  ...
});
    example

    Handle child ordering changes:

    ref.on('child_moved', function(childSnapshot, prevChildKey) {
  ...
});

    Parameters

    • eventType: EventType

      One of the following strings: "value", "child_added", "child_changed", "child_removed", or "child_moved."

    • callback: (a: DataSnapshot, b?: string | null) => any

      A callback that fires when the specified event occurs. The callback will be passed a DataSnapshot. For ordering purposes, "child_added", "child_changed", and "child_moved" will also be passed a string containing the key of the previous child, by sort order, or null if it is the first child.

    • Optional cancelCallbackOrContext: ((a: Error) => any) | Object | null

      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.

    • Optional context: Object | null

      If provided, this object will be used as this when calling your callback(s).

    Returns (a: DataSnapshot | null, b?: string | null) => any

    The provided callback function is returned unmodified. This is just for convenience if you want to pass an inline function to on() but store the callback function for later passing to off().

      • Parameters

        Returns any

onDisconnect

once

  • once ( eventType :  EventType ,  successCallback ? :  ( a :  DataSnapshot ,  b ? :  string | null ) => any ,  failureCallbackOrContext ? :  ( ( a :  Error ) => void ) | Object | null ,  context ? :  Object | null ) : Promise < DataSnapshot >

  • Listens for exactly one event of the specified event type, and then stops listening.

    This is equivalent to calling on(), and then calling off() inside the callback function. See on() for details on the event types.

    example
    // Basic usage of .once() to read the data located at ref.
ref.once('value')
  .then(function(dataSnapshot) {
    // handle read data.
  });

    Parameters

    • eventType: EventType

      One of the following strings: "value", "child_added", "child_changed", "child_removed", or "child_moved."

    • Optional successCallback: (a: DataSnapshot, b?: string | null) => any

      A callback that fires when the specified event occurs. The callback will be passed a DataSnapshot. For ordering purposes, "child_added", "child_changed", and "child_moved" will also be passed a string containing the key of the previous child by sort order, or null if it is the first child.

    • Optional failureCallbackOrContext: ((a: Error) => void) | Object | null

      An optional callback that will be notified if your client does not have permission to read the data. This callback will be passed an Error object indicating why the failure occurred.

    • Optional context: Object | null

      If provided, this object will be used as this when calling your callback(s).

    Returns Promise<DataSnapshot>

orderByChild

  • orderByChild ( path :  string ) : Query

  • Generates a new Query object ordered 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 .indexOn rule for more information.

    You can read more about orderByChild() in Sort data.

    example
    var ref = firebase.database().ref("dinosaurs");
ref.orderByChild("height").on("child_added", function(snapshot) {
  console.log(snapshot.key + " was " + snapshot.val().height + " m tall");
});

    Parameters

    • path: string

    Returns Query

orderByKey

  • orderByKey ( ) : Query

  • Generates a new Query object ordered by key.

    Sorts the results of a query by their (ascending) key values.

    You can read more about orderByKey() in Sort data.

    example
    var ref = firebase.database().ref("dinosaurs");
ref.orderByKey().on("child_added", function(snapshot) {
  console.log(snapshot.key);
});

    Returns Query

orderByPriority

  • orderByPriority ( ) : Query

  • Generates a new Query object ordered by priority.

    Applications need not use priority but can order collections by ordinary properties (see Sort data for alternatives to priority.

    Returns Query

orderByValue

  • orderByValue ( ) : Query

  • Generates a new Query object ordered 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 Sort data.

    example
    var scoresRef = firebase.database().ref("scores");
scoresRef.orderByValue().limitToLast(3).on("value", function(snapshot) {
  snapshot.forEach(function(data) {
    console.log("The " + data.key + " score is " + data.val());
  });
});

    Returns Query

push

  • push ( value ? :  any ,  onComplete ? :  ( a :  Error | null ) => any ) : ThenableReference

  • 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 Append to a list of data
    See The 2^120 Ways to Ensure Unique Identifiers

    example
    var messageListRef = firebase.database().ref('message_list');
var newMessageRef = messageListRef.push();
newMessageRef.set({
  'user_id': 'ada',
  'text': 'The Analytical Engine weaves algebraical patterns just as the Jacquard loom weaves flowers and leaves.'
});
// We've appended a new message to the message_list location.
var path = newMessageRef.toString();
// path will be something like
// 'https://sample-app.firebaseio.com/message_list/-IKo28nwJLH0Nc5XeFmj'

    Parameters

    • Optional value: any

      Optional value to be written at the generated location.

    • Optional onComplete: (a: Error | null) => any

      Callback called when write to server is complete.

        • Parameters

          Returns any

    Returns ThenableReference

    Combined Promise and Reference; resolves when write is complete, but can be used immediately as the Reference to the child location.

remove

  • remove ( onComplete ? :  ( a :  Error | null ) => void ) : Promise < void >

  • 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.

    example
    var adaRef = firebase.database().ref('users/ada');
adaRef.remove()
  .then(function() {
    console.log("Remove succeeded.")
  })
  .catch(function(error) {
    console.log("Remove failed: " + error.message)
  });

    Parameters

    • Optional onComplete: (a: Error | null) => void

      Callback called when write to server is complete.

        • (a: Error | null): void

        • Parameters

          Returns void

    Returns Promise<void>

    Resolves when remove on server is complete.

set

  • set ( value :  any ,  onComplete ? :  ( a :  Error | null ) => void ) : Promise < void >

  • 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.

    example
    var adaNameRef = firebase.database().ref('users/ada/name');
adaNameRef.child('first').set('Ada');
adaNameRef.child('last').set('Lovelace');
// We've written 'Ada' to the Database location storing Ada's first name,
// and 'Lovelace' to the location storing her last name.
    example
    adaNameRef.set({ first: 'Ada', last: 'Lovelace' });
// Exact same effect as the previous example, except we've written
// Ada's first and last name simultaneously.
    example
    adaNameRef.set({ first: 'Ada', last: 'Lovelace' })
  .then(function() {
    console.log('Synchronization succeeded');
  })
  .catch(function(error) {
    console.log('Synchronization failed');
  });
// Same as the previous example, except we will also log a message
// when the data has finished synchronizing.

    Parameters

    • value: any

      The value to be written (string, number, boolean, object, array, or null).

    • Optional onComplete: (a: Error | null) => void

      Callback called when write to server is complete.

        • (a: Error | null): void

        • Parameters

          Returns void

    Returns Promise<void>

    Resolves when write to server is complete.

setPriority

  • setPriority ( priority :  string | number | null ,  onComplete :  ( a :  Error | null ) => void ) : 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 Sorting and filtering data).

    Parameters

    • priority: string | number | null
    • onComplete: (a: Error | null) => void
        • (a: Error | null): void

        • Parameters

          Returns void

    Returns Promise<void>

setWithPriority

  • setWithPriority ( newVal :  any ,  newPriority :  string | number | null ,  onComplete ? :  ( a :  Error | null ) => void ) : Promise < void >

  • 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 Sorting and filtering data).

    Parameters

    • newVal: any
    • newPriority: string | number | null
    • Optional onComplete: (a: Error | null) => void
        • (a: Error | null): void

        • Parameters

          Returns void

    Returns Promise<void>

startAfter

  • startAfter ( value :  number | string | boolean | null ,  key ? :  string ) : Query

  • Creates a Query 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.

    example
    // Find all dinosaurs that are more than three meters tall.
var ref = firebase.database().ref("dinosaurs");
ref.orderByChild("height").startAfter(3).on("child_added", function(snapshot) {
  console.log(snapshot.key)
});

    Parameters

    • value: number | string | boolean | null

      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.

    • Optional key: string

      The child key to start after. This argument is only allowed if ordering by child, value, or priority.

    Returns Query

startAt

  • startAt ( value :  number | string | boolean | null ,  key ? :  string ) : Query

  • Creates a Query 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 Filtering data.

    example
    // Find all dinosaurs that are at least three meters tall.
var ref = firebase.database().ref("dinosaurs");
ref.orderByChild("height").startAt(3).on("child_added", function(snapshot) {
  console.log(snapshot.key)
});

    Parameters

    • value: number | string | boolean | null

      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.

    • Optional key: string

      The child key to start at. This argument is only allowed if ordering by child, value, or priority.

    Returns Query

toJSON

  • toJSON ( ) : Object

  • Returns a JSON-serializable representation of this object.

    Returns Object

    A JSON-serializable representation of this object.

toString

  • toString ( ) : 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 firebase.database().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.

    example
    // Calling toString() on a root Firebase reference returns the URL where its
// data is stored within the Database:
var rootRef = firebase.database().ref();
var rootUrl = rootRef.toString();
// rootUrl === "https://sample-app.firebaseio.com/".

// Calling toString() at a deeper Firebase reference returns the URL of that
// deep path within the Database:
var adaRef = rootRef.child('users/ada');
var adaURL = adaRef.toString();
// adaURL === "https://sample-app.firebaseio.com/users/ada".

    Returns string

    The absolute URL for this location.

transaction

  • transaction ( transactionUpdate :  ( a :  any ) => any ,  onComplete ? :  ( a :  Error | null ,  b :  boolean ,  c :  DataSnapshot | null ) => void ,  applyLocally ? :  boolean ) : Promise < TransactionResult >

  • 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, transaction() 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 transaction() 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 transaction() 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.

    example
    // Increment Ada's rank by 1.
var adaRankRef = firebase.database().ref('users/ada/rank');
adaRankRef.transaction(function(currentRank) {
  // If users/ada/rank has never been set, currentRank will be `null`.
  return currentRank + 1;
});
    example
    // Try to create a user for ada, but only if the user id 'ada' isn't
// already taken
var adaRef = firebase.database().ref('users/ada');
adaRef.transaction(function(currentData) {
  if (currentData === null) {
    return { name: { first: 'Ada', last: 'Lovelace' } };
  } else {
    console.log('User ada already exists.');
    return; // Abort the transaction.
  }
}, function(error, committed, snapshot) {
  if (error) {
    console.log('Transaction failed abnormally!', error);
  } else if (!committed) {
    console.log('We aborted the transaction (because ada already exists).');
  } else {
    console.log('User ada added!');
  }
  console.log("Ada's data: ", snapshot.val());
});

    Parameters

    • transactionUpdate: (a: any) => any

      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.

        • (a: any): any

        • Parameters

          • a: any

          Returns any

    • Optional onComplete: (a: Error | null, b: boolean, c: DataSnapshot | null) => void

      A callback function that will be called when the transaction completes. The callback is passed three arguments: a possibly-null Error, a boolean indicating whether the transaction was committed, and a DataSnapshot indicating the final result. If the transaction failed abnormally, the first argument will be an Error object indicating the failure cause. If the transaction finished normally, but no data was committed because no data was returned from transactionUpdate, then second argument will be false. If the transaction completed and committed data to Firebase, the second argument will be true. Regardless, the third argument will be a DataSnapshot containing the resulting data in this location.

    • Optional applyLocally: boolean

      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.

    Returns Promise<TransactionResult>

    Returns a Promise that can optionally be used instead of the onComplete callback to handle success and failure.

update

  • update ( values :  Object ,  onComplete ? :  ( a :  Error | null ) => void ) : Promise < 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 Introducing multi-location updates and more.

    example
    var adaNameRef = firebase.database().ref('users/ada/name');
// Modify the 'first' and 'last' properties, but leave other data at
// adaNameRef unchanged.
adaNameRef.update({ first: 'Ada', last: 'Lovelace' });

    Parameters

    • values: Object

      Object containing multiple values.

    • Optional onComplete: (a: Error | null) => void

      Callback called when write to server is complete.

        • (a: Error | null): void

        • Parameters

          Returns void

    Returns Promise<void>

    Resolves when update on server is complete.