Question 59529650

controllers.application.js

import Ember from 'ember';
import EmberObject, { set } from '@ember/object';
import ArrayProxy from '@ember/array/proxy';
import { Promise, resolve, all } from 'rsvp';

const section = EmberObject.create();
const log = ArrayProxy.create({ content: [] });

export default Ember.Controller.extend({
  appName: 'Question 59529650',
  
  chainLength: 0,
  promisesRunning: 0,
  log,
  section,
  
  someAction() {
    var section = this.section;
    var myPendingPromise = section.myPendingPromise || resolve();
    myPendingPromise = myPendingPromise.then(() => {
      return this.myCustomPromise();
    });
    set(section, 'myPendingPromise', myPendingPromise);
    this.incrementProperty('chainLength');
  },

  myCustomPromise() {
    return new Promise(resolve => {
      this.incrementProperty('promisesRunning');
      this.log.pushObject('Promise started');
      setTimeout(() => {
        this.decrementProperty('chainLength');
        this.decrementProperty('promisesRunning');
        this.log.pushObject('Promise resolved'); 
        resolve(true)
      }, 2000);
    });
  },
});

templates.application.hbs

<h1>{{appName}}</h1>
<p><a href="https://stackoverflow.com/questions/59529650/how-do-i-understand-this-custom-use-of-promise-in-code">https://stackoverflow.com/questions/59529650/how-do-i-understand-this-custom-use-of-promise-in-code</a></p>
<p>Click button fast few times to see how it fills up promise chain</p>
<br>
Promise chain length: {{chainLength}}; Promises currently running: {{promisesRunning}}
<br>
<br>
<button onclick={{action someAction}}>Click me to add promise into chain</button>
<br>
<br>
<h2>Log</h2>
{{#each log as |item|}}<p>{{item}}</p>{{/each}}
{{outlet}}
<br>
<br>

twiddle.json

{
  "version": "0.15.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.4.3",
    "ember-template-compiler": "3.4.3",
    "ember-testing": "3.4.3"
  },
  "addons": {
    "ember-data": "3.4.2"
  }
}