Implement a Promise Queue (TaskQueue) with concurrency

Question

Accepted Answer

**Approach:** Similar to p-limit but as a class with `add`, `pause`, `onIdle`.

```javascript
class TaskQueue {
  constructor(concurrency = 2) { this.concurrency = concurrency; this.running = 0; this.queue = []; this.paused = false; }
  add(task) {
    return new Promise((resolve, reject) => {
      this.queue.push({ task, resolve, reject });
      this._next();
    });
  }
  _next() {
    if (this.paused || this.running >= this.concurrency || this.queue.length === 0) return;
    this.running++;
    const { task, resolve, reject } = this.queue.shift();
    Promise.resolve().then(task).then(resolve, reject).finally(() => { this.running--; this._next(); });
  }
  pause() { this.paused = true; }
  resume() { this.paused = false; this._next(); }
  onIdle() {
    if (this.running === 0 && this.queue.length === 0) return Promise.resolve();
    return new Promise(r => { const check = () => { if (this.running === 0 && this.queue.length === 0) r(); else setTimeout(check, 10); }; check(); });

Implement a Promise Queue (TaskQueue) with concurrency

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KEEP THE
STREAK ALIVE.

Understand the problem

Attempt it yourself

Study the solution

Solution ready — 2 min read

Join the discussion

Discussion (0)

KEEP THESTREAK ALIVE.

KEEP THE
STREAK ALIVE.