Promise Queue

PromiseQueue.js

var delay = (seconds) => new Promise((resolves) => {
    setTimeout(function(){
      console.log(seconds);
      resolves();
    }, seconds*1000);
});

var tasks = [
  delay(2),
  delay(4),
  delay(6),
  delay(8),
  delay(10)
];

class PromiseQueue {

  constructor(promises=[], concurrentCount=1) {
    this.concurrent = concurrentCount;
    this.total = promises.length;
    this.todo = promises;
    this.running = [];
    this.complete = [];
  }

  get runAnother() {
    return (this.running.length < this.concurrent) && this.todo.length;
  }

  graphTasks() {
    var { todo, running, complete } = this;
    console.log(`
     todo: [${todo.map( () => 'X')}]
     running: [${running.map( () => 'X')}]
     complete: [${complete.map( () => 'X')}]
    `);
  }

  run() {
    while (this.runAnother) {
      var promise = this.todo.shift();
      promise.then(() => {
        this.complete.push(this.running.shift());
        this.graphTasks();
        this.run();
      })
      this.running.push(promise);
      this.graphTasks();
    }
  }

}

delayQueue = new PromiseQueue(tasks, 2);
delayQueue.run();