Wait for variable to become true - in promise

promise-wait.js

window.testVar = null;

function waitForCondition (variable) {
  function waitFor(result) {
    if (result) {
      return result;
    }
    return new Promise((resolve) => setTimeout(resolve, 100))
      .then(() => Promise.resolve(window[variable])) 
      .then((res) => waitFor(res));
  }
  return waitFor();
}

waitForCondition('testVar').then((res) => console.log('>>>', res));