Adding share, shareValue, and shareReplay.

Adding the share(), shareValue(), and shareReplay() methods. These methods are optimized for the 80% case, in which the developer simply wants to share side effects among multiple concurrent observer. This allows developers simple code like this:

var interval = Rx.Observable.interval(1000);

var source = interval
    .take(2)
    .doAction(
        function (x) { 
            console.log('Side effect');
        })
     .share();
 
// When the number of observers subscribed to published observable goes from 
// 0 to 1, we connect to the underlying observable sequence.
source.subscribe(createObserver('SourceA'));
// When the second subscriber is added, no additional subscriptions are added to the
// underlying observable sequence. As a result the operations that result in side 
// effects are not repeated per subscriber.
source.subscribe(createObserver('SourceB'));

function createObserver(tag) {
    return Rx.Observer.create(
        function (x) {
            console.log('Next: ' + tag + x);
        },
        function (err) {
            console.log('Error: ' + err);   
        },
        function () {
            console.log('Completed');   
        });
}