Subscribing to an observable in angular2

• Observable are similar to promises but with major difference that make them better.
• Observables is an ES7 feature which means you need to make use of an external library to use it today. RxJS is a good one. RxJS also provides Observable operators which you can use to manipulate the data being emitted. Some of these operators are:

• Map
• Filter
• Take
• Skip
• Debounce

• When we use observable we simply replace "then with subscribe".The value function is called for each value the observable emits

        //subscribe to the observable
     .subscribe(products => this.products=products,
                error =>this.errorMessage=<any>error);

         I

•       It provides an third handler that is executed on completion . This option is usually not used

 //subscribe to the observable
     .subscribe(products => this.products=products,
                error =>this.errorMessage=<any>error,

                completeFn);

• The subscribe function returns a subscription. We can use this to call unsubscribe and cancel the subscription

Note:

• Observable are lazy and are not called unless we use subscribe
• http call are single asynchronous operations only one item is emitted that is the http response object