[RxJS] BehaviorSubject

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);