behaviorsubject.md

This is RxJS v 4. Find the latest version here

Rx.BehaviorSubject class

Represents a value that changes over time. Observers can subscribe to the subject to receive the last (or initial) value and all subsequent notifications. If you are looking for BehaviorSubject without initial value see Rx.ReplaySubject.

This class inherits both from the Rx.Observable and Rx.Observer classes.

Usage

The follow example shows the basic usage of an Rx.BehaviorSubject class.

/* Initialize with initial value of 42 */
var subject = new Rx.BehaviorSubject(42);

var subscription = subject.subscribe(
    function (x) {
        console.log('Next: ' + x.toString());
    },
    function (err) {
        console.log('Error: ' + err);
    },
    function () {
        console.log('Completed');
    });

// => Next: 42

subject.onNext(56);
// => Next: 56

subject.onCompleted();
// => Completed

Location

• rx.binding.js

BehaviorSubject Constructor

• constructor

BehaviorSubject Instance Methods

• dispose
• getValue
• hasObservers

Inherited Classes

• Rx.Observable
• Rx.Observer

BehaviorSubject Constructor

Rx.BehaviorSubject(initialValue)

# Ⓢ

Initializes a new instance of the Rx.BehaviorSubject class which creates a subject that caches its last value and starts with the specified value.

Arguments

1. initialValue (Any): Initial value sent to observers when no other value has been received by the subject yet.

Example

var subject = new Rx.BehaviorSubject(56);

subject.onCompleted();

var subscription = subject.subscribe(
    function (x) {
        console.log('Next: ' + x);
    },
    function (err) {
        console.log('Error: ' + err);
    },
    function () {
        console.log('Completed');
    });

// => Next: 56

subject.onNext(42);
// => Next: 42

subject.onCompleted();
// => Completed

Location

= rx.binding.js

---

BehaviorSubject Instance Methods

Rx.BehaviorSubject.prototype.dispose()

# Ⓢ

Unsubscribe all observers and release resources.

Example

var subject = new Rx.BehaviorSubject();

var subscription = subject.subscribe(
    function (x) {
        console.log('Next: ' + x.toString());
    },
    function (err) {
        console.log('Error: ' + err);
    },
    function () {
        console.log('Completed');
    });

subject.onNext(42);
// => Next: 42

subject.onCompleted();
// => Completed

subject.dispose();

try {
	subject.onNext(56);
} catch (e) {
	console.log(e.message);
}

// => Object has been disposed

Location

= rx.binding.js

---

Rx.BehaviorSubject.prototype.getValue()

# Ⓢ

Gets the current value or throws an exception. Value is frozen after onCompleted is called. After onError is called always throws the specified exception. An exception is always thrown after dispose is called.

Returns

(Mixed): The initial value passed to the constructor until onNext is called; after which, the last value passed to onNext.

Example

var subject = new Rx.BehaviorSubject(56);

console.log('Value is: ' + subject.getValue());

// => Value is: 56

subject.onNext(42);

console.log('Value is: ' + subject.getValue());

// => Value is: 42

subject.onCompleted();

subject.onNext(100);

console.log('Value is frozen: ' + subject.getValue());

// => Value is frozen: 42

subject.dispose();

try {
    subject.getValue();
} catch (e) {
    console.log(e.message);
}

// => Object has been disposed

Location

= rx.binding.js

---

Rx.BehaviorSubject.prototype.hasObservers()

# Ⓢ

Indicates whether the subject has observers subscribed to it.

Returns

(Boolean): Returns true if the Subject has observers, else false.

Example

var subject = new Rx.BehaviorSubject();

console.log(subject.hasObservers());

// => false

var subscription = subject.subscribe(
    function (x) {
        console.log('Next: ' + x.toString());
    },
    function (err) {
        console.log('Error: ' + err);
    },
    function () {
        console.log('Completed');
    });

console.log(subject.hasObservers());

// => true

Location

= rx.binding.js

---