gistfile1.js

Array.prototype.oldPush = Array.prototype.push;
Array.prototype.push = function(val) {
  if (this.length > 3)
    alert("wtfbbq - " + this);
  this.oldPush(val);
};

var foo = [];
var bar = [1,2,3,4,5];
for (var i = 0; i < bar.length; i++) {
  foo.push(bar[i]);
}
foo = foo.join('');
alert(foo);