Add to a javascript function

Question

I have a function I can't modify:

function addToMe() { doStuff(); } 

Can I add to this function? Obviously this syntax is terribly wrong but it's the general idea...

function addToMe() { addToMe() + doOtherStuff(); } 

Answer 1

You could store a reference to the original function, and then override it, with a function that calls back the original one, and adds the functionality you desire:

var originalFn = addToMe;  addToMe = function () {   originalFn(); // call the original function   // other stuff }; 

You can do this because JavaScript functions are first-class objects.

Edit: If your function receives arguments, you should use apply to pass them to the original function:

addToMe = function () {   originalFn.apply(this, arguments); // preserve the arguments   // other stuff }; 

You could also use an auto-executing function expression with an argument to store the reference of the original function, I think it is a little bit cleaner:

addToMe = (function (originalFn) {   return function () {     originalFn.apply(originalFn, arguments); // call the original function     // other stuff   }; })(addToMe); // pass the reference of the original function