Test

gistfile1.txt

function wait(milliseconds) {
  return new Promise((resolve, reject) => {
    setTimeout(resolve, milliseconds);
  });
}

function waitForSelector(selector) {
  const wait = new Promise((resolve, reject) => {
    let checkExist = setInterval(function () {
      if (document.querySelector(selector)) {
        clearInterval(checkExist);
        resolve();
      }
    }, 100);
  });

  return wait;
}