promise.js

class DoStuff {
  
  runAnimation() {
    return new Promise((resolve, reject) => {
      
      const run = true;
      
      const step = () => {
        if (run) {
          run = this._doSomething();
          requestAnimationFrame(step);
        } else {
          resolve();
        }
      }
      
      step();
    });
  }
}