Observables in Angular

You may already know that JavaScript is implemented as a single-threaded event loop, making it synchronous. Thus, no two script codes can run in parallel. Angular applications can make use of a Promise, which is part of ECMAScript 6, or Observables from RxJS, for handling asynchronous data. In the near future, Observables may also be made part of standard JavaScript.

A Promise allows you to define handlers for an asynchronous event's eventual completion. We used a Promise in Chapter 10, Angular Forms, too, for performing asynchronous validation. Here's a sample snippet for using a Promise:

return newPromise( (resolve, reject) => {            
      if (/* some condition */) {
resolve("success");
      }
reject("failed");            
});

The function passed to a promise is an executor function that would perform some asynchronous operations and, on completion, call resolve or reject based on success or failure respectively.

Observables are another option for asynchronous...