Promise Async Calls to Prevent Race Conditions

gistfile1.js

/**
 * calculatePromise() Use promises to get x and y values, now we can run our 
 * async tasks in parallel using Promise.all. Once we have both values
 */
function calculatePromise() {
  var y = new Promise((resolve, reject) => {
    setTimeout(() => resolve(2), Math.random() * 1000);
  });

  var x = new Promise((resolve, reject) => {
    setTimeout(() => resolve(2), Math.random() * 1000);
  });
  
  //Get values of y and x and then calulate z
  Promise.all([y, x])
    .then(result => result[0] + result[1])
    .then(z => console.log(z));
}

//Lets run it a 100 times. This out simulate us refreshing the browser a few times.
for (let i = 0; i < 100; i++) {
  calculateZ();
}

//Success! We've run both asyncs in parallel and correctly calculate z everytime!