Monday, February 13, 2017

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);

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

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