utilities/makeHot.js

  1. import { Observable } from '../Observable';
  2. import { Subject } from '../Subject';
  4. /**
  5.  * Makes an observable "hot" -- very useful for things like DOM event listeners
  6.  * so that the events do not get bound numerous amounts of times
  7.  * 
  8.  * @memberof utilities
  9.  *
  10.  * @param {Observable} cold$
  11.  * @returns {Observable}
  12.  */
  13. export const makeHot = (cold$) => {
  14.   const subject = new Subject();
  15.   let mainSub = cold$.subscribe(subject);
  16.   let refs = 0;
  17.   
  18.   return new Observable((observer) => {
  19.     refs++;
  20.     
  21.     // if the main subscription is complete we have to resubscribe to it
  22.     if (mainSub.isComplete) {
  23.       mainSub = cold$.subscribe(subject);
  24.     }
  25.     
  26.     let sub = subject.subscribe(observer);
  27.     
  28.     return () => {
  29.       refs--;
  30.       if (refs === 0) mainSub.unsubscribe();
  31.       sub.unsubscribe();
  32.     };
  33.   });
  34. };
  36. Observable.prototype.makeHot = function () {
  37.   return makeHot(this);
  38. };