Make a Spy

example.js

// a highly simplified version of a spy which counts total call 
var spy = function(object, property){
  var origFn = object[property]; 
  
  var spyFn = function(){
    spyFn.callCount++;
    return origin.apply(object, arguments);
  }
  spyFn.callCount = 0;
  object[property] = spyFn;
  
  return spyFn;
}