[RxJS] BehaviorSubject: representing a value over time

When an Observer subscribe to a BehaviorSubject. It receivces the last emitted value and then all the subsequent values. BehaviorSubject requires that we provide a starting value, so taht all Observers will always receive a value when they subscribe to a BehaviorSubject.

Imagine we want to retreve a remote file and print its contents on an HTML page, but we wnat placeholder text while we wait for the contents. We can use a BehaviorSubject for this.

var subject = new Rx.BehaviorSubject('Waiting for content');

subject.subscribe(

function(result) {

  document.body.textContent = result.response || result;

},

function(err) {

  document.body.textContent = 'There was an error retrieving content';

}

);

Rx.DOM.get('/remote/content').subscribe(subject);

Example 2:

var subject = new Rx.BehaviorSubject();

var observerA = {

  next: function (x) { console.log('A next ' + x); },

  error: function (err) { console.log('A error ' + err); },

  complete: function () { console.log('A done'); },

};

subject.subscribe(observerA);

console.log('observerA subscribed');

var observerB = {

  next: function (x) { console.log('B next ' + x); },

  error: function (err) { console.log('B error ' + err); },

  complete: function () { console.log('B done'); },

};

subject.next();

subject.next();

subject.next();

/*

0---1---2---3---------------

 0..1...2...3...

                      3.....

*/

setTimeout(function () {

  subject.subscribe(observerB);

  console.log('observerB subscribed');

}, );

/*

"A next 0"  <-- Always get the init value

"observerA subscribed"

"A next 1"

"A next 2"

"A next 3"

"B next 3" <-- Because A & B share the same observer, B will receive last emit value

"observerB subscribed"

*/

巴特西

[RxJS] BehaviorSubject: representing a value over time

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