One-stop understanding of Promises...

index.js

//TL;DR - Read the MDN page and skip all the tutorials: 
// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise

//ES6 
var x = new Promise((resolve, reject) => {
        setTimeout(function () { resolve('test'); }, 5000);
    });

x.then((msg) => console.log(msg));

//result - after 5 seconds, writes 'test' to STDOUT and exits