Taskqueue with given concurrency

ASyncTaskQueue.js

class AsyncTaskQueue {
  constructor(concurrency) {
    this.concurrency = concurrency;
    this.running = 0;
    this.queue = [];
  }

  pushtask(task) {
    this.queue.push(task);
    process.nextTick(this.next.bind(this));
    return this;
  }

  next() {
    while (this.running < this.concurrency && this.queue.length) {
      const task = this.queue.shift();
      task(() => {
        this.running--;
        process.nextTick(this.next.bind(this));
      });
      this.running++;
    }
  }
}

function makeSimpleTask(name) {
  return (cb) => {
    console.log("started", name);
    setTimeout(() => {
      console.log(name, "completed");
      cb();
    }, Math.random() * 2000);
  };
}

const taskQueue = new AsyncTaskQueue(3);

taskQueue.pushtask(makeSimpleTask("task 1"));
taskQueue.pushtask(makeSimpleTask("task 2"));
taskQueue.pushtask(makeSimpleTask("task 3"));
taskQueue.pushtask(makeSimpleTask("task 4"));
taskQueue.pushtask(makeSimpleTask("task 5"));