operators/toPromise.js

  1. import { Observable } from '../Observable';
  2. import { first } from './first';
  4. /**
  5.  * Reverse of [`fromPromise`](#frompromise)
  6.  * <br />
  7.  * Converts an Observable to a promise, takes the first value and then completes
  8.  * 
  9.  * @memberof operators
  10.  *
  11.  * @param {Observable} source$
  12.  * @returns {Promise<*>}
  13.  */
  14. export const toPromise = function (source$) {
  15.   if (!global.Promise) {
  16.     throw new Error('Promise does not exist in the current context');
  17.   }
  18.   
  19.   return new Promise(function (respond, reject) {
  20.     return first(source$).subscribe({
  21.       next: respond,
  22.       error: reject,
  23.       complete: respond,
  24.     });
  25.   });
  26. };
  28. Observable.toPromise = toPromise;
  29. Observable.prototype.toPromise = function () {
  30.   return toPromise(this);
  31. };