Can you alter a Javascript function after declaring it?

Question

Let's say I have var a = function() { return 1; }. Is it possible to alter a so that a() returns 2? Perhaps by editing a property of the a object, since every function is an object?

Update: Wow, thanks for all the responses. However, I'm afraid I wasn't looking to simply reassign a variable but actually edit an existing function. I am thinking along the lines of how you can combine partial functions in Scala to create a new PartialFunction. I am interested in writing something similar in Javascript and was thinking that the existing function could perhaps be updated, rather than creating an entirely new Function object.

Answer 1

You can do all kinds of fun stuff with javascript, including redefining functions:

let a = function() { return 1; } console.log(a()); // 1      // keep a reference let old = a;     // redefine a = function() {   // call the original function with any arguments specified, storing the result   const originalResult = old.apply(old, arguments);   // add one   return originalResult + 1; };  console.log(a()); // 2 

Voila.

Edit: Updated to show this in a crazier scenario:

let test = new String("123"); console.log(test.toString()); // logs 123 console.log(test.substring(0)); // logs 123 String.prototype.substring = function(){ return "hahanope"; } console.log(test.substring(0)); // logs hahanope 

You can see here that even though "test" is defined first, and we redefine substring() afterwards, the change still applies.

Side note: you really should reconsider your architecture if you're doing this...you're going to confuse the crap out of some poor developer 5 years down the road when s/he's looking at a function definition that's supposed to return 1, but seems to always return 2....