Cllaback
https://github.com/eu81273/jsfiddle-console
HTML
<script src="https://rawgit.com/eu81273/jsfiddle-console/master/console.js"></script>JavaScript
//Rediscovering Promises in Javascript
//https://medium.com/@dimpapadim3/promises-made-simple-in-javascript-db9e3bc39537
var square = (x,callback)=>callback(x*x);
square(2,x=>square(x,console.log)); // prints 16