the most basic example of an async cb in es5 (the old way)

asyncCB_es5.js

//the most basic async cb in es5
var sleep = function(ms) {
  var promise = new Promise(function(resolve, reject) {
    setTimeout(function() {
      resolve("the result");
    }, ms);
  });

  return promise;

};

var promise = sleep(2000, function(result) {
  console.log(result);
});