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DataSnapshot class

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).

Signature:

typescript

export declare class DataSnapshot

Properties

Property	Type	Description
key	string \| null	The key (last part of the path) of the location of this <code>DataSnapshot</code>.<!-- -->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 <code>DataSnapshot</code> will return the key for the location that generated it. However, accessing the key on the root URL of a Database will return <code>null</code>.
priority	string \| number \| null	Gets the priority value of the data in this <code>DataSnapshot</code>.<!-- -->Applications need not use priority but can order collections by ordinary properties (see Sorting and filtering data ).
ref	DatabaseReference	The location of this DataSnapshot.
size	number	Returns the number of child properties of this <code>DataSnapshot</code>.

Methods

Method	Modifiers	Description
child(path)		Gets another <code>DataSnapshot</code> for the location at the specified relative path.<!-- -->Passing a relative path to the <code>child()</code> method of a DataSnapshot returns another <code>DataSnapshot</code> 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 <code>DataSnapshot</code> (that is, a <code>DataSnapshot</code> whose value is <code>null</code>) is returned.
exists()		Returns true if this <code>DataSnapshot</code> contains any data. It is slightly more efficient than using <code>snapshot.val() !== null</code>.
exportVal()		Exports the entire contents of the DataSnapshot as a JavaScript object.<!-- -->The <code>exportVal()</code> method is similar to <code>val()</code>, except priority information is included (if available), making it suitable for backing up your data.
forEach(action)		Enumerates the top-level children in the <code>IteratedDataSnapshot</code>.<!-- -->Because of the way JavaScript objects work, the ordering of data in the JavaScript object returned by <code>val()</code> is not guaranteed to match the ordering on the server nor the ordering of <code>onChildAdded()</code> events. That is where <code>forEach()</code> comes in handy. It guarantees the children of a <code>DataSnapshot</code> will be iterated in their query order.<!-- -->If no explicit <code>orderBy*()</code> method is used, results are returned ordered by key (unless priorities are used, in which case, results are returned by priority).
hasChild(path)		Returns true if the specified child path has (non-null) data.
hasChildren()		Returns whether or not the <code>DataSnapshot</code> has any non-<code>null</code> child properties.<!-- -->You can use <code>hasChildren()</code> to determine if a <code>DataSnapshot</code> has any children. If it does, you can enumerate them using <code>forEach()</code>. If it doesn't, then either this snapshot contains a primitive value (which can be retrieved with <code>val()</code>) or it is empty (in which case, <code>val()</code> will return <code>null</code>).
toJSON()		Returns a JSON-serializable representation of this object.
val()		Extracts a JavaScript value from a <code>DataSnapshot</code>.<!-- -->Depending on the data in a <code>DataSnapshot</code>, the <code>val()</code> method may return a scalar type (string, number, or boolean), an array, or an object. It may also return null, indicating that the <code>DataSnapshot</code> is empty (contains no data).

DataSnapshot.key

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.

Signature:

typescript

get key(): string | null;

DataSnapshot.priority

Gets the priority value of the data in this DataSnapshot.

Applications need not use priority but can order collections by ordinary properties (see Sorting and filtering data ).

Signature:

typescript

get priority(): string | number | null;

DataSnapshot.ref

The location of this DataSnapshot.

Signature:

typescript

readonly ref: DatabaseReference;

DataSnapshot.size

Returns the number of child properties of this DataSnapshot.

Signature:

typescript

get size(): number;

DataSnapshot.child()

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.

Signature:

typescript

child(path: string): DataSnapshot;

Parameters

Parameter	Type	Description
path	string	A relative path to the location of child data.

Returns:

DataSnapshot

DataSnapshot.exists()

Returns true if this DataSnapshot contains any data. It is slightly more efficient than using snapshot.val() !== null.

Signature:

typescript

exists(): boolean;

Returns:

boolean

DataSnapshot.exportVal()

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.

Signature:

typescript

exportVal(): any;

Returns:

any

The DataSnapshot's contents as a JavaScript value (Object, Array, string, number, boolean, or null).

DataSnapshot.forEach()

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).

Signature:

typescript

forEach(action: (child: IteratedDataSnapshot) => boolean | void): boolean;

Parameters

Parameter	Type	Description
action	(child: IteratedDataSnapshot<!-- -->) => boolean \| void	A function that will be called for each child DataSnapshot. The callback can return true to cancel further enumeration.

Returns:

boolean

true if enumeration was canceled due to your callback returning true.

DataSnapshot.hasChild()

Returns true if the specified child path has (non-null) data.

Signature:

typescript

hasChild(path: string): boolean;

Parameters

Parameter	Type	Description
path	string	A relative path to the location of a potential child.

Returns:

boolean

true if data exists at the specified child path; else false.

DataSnapshot.hasChildren()

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).

Signature:

typescript

hasChildren(): boolean;

Returns:

boolean

true if this snapshot has any children; else false.

DataSnapshot.toJSON()

Returns a JSON-serializable representation of this object.

Signature:

typescript

toJSON(): object | null;

Returns:

object | null

DataSnapshot.val()

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).

Signature:

typescript

val(): any;

Returns:

any

The DataSnapshot's contents as a JavaScript value (Object, Array, string, number, boolean, or null).