Method for finding out the refresh rate of the device

refresh-rate.js

 function _getRefreshRate() {
    const rafPromise = _ => new Promise(requestAnimationFrame);
    const idlePromise = _ => new Promise(requestIdleCallback);

    let f1, f2;

    return new Promise(resolve => {
      idlePromise()
      .then(_ => rafPromise())
      .then(frame => {f1 = frame; return rafPromise();})
      .then(frame => {f2 = frame; return rafPromise();})
      .then(_ => {
        const ft = f2 - f1;
        const fps = Math.ceil(1000 / ft);
        console.log(`Refresh rate should be ${fps}Hz`);
        resolve();
      });
    });
  }