the asynchronous callback -- the most absolute basic example using the setTimeout and setInterval functions on the client

pattern_asynchronousCallback.js

 whenDone = function () {
    console.log ("done")
   };
   
   doWork = function(callback) {
     //do some work
     setTimeout(callback, 3000); //put the call back on the event loop by 3 seconds (during this time, other work is being done)
   };