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

Answer 1

I used something like this to modify an existing function whose declaration was not accessible to me:

// declare function foo
var foo = function (a) { alert(a); };

// modify function foo
foo = new Function (
  "a",
  foo.toSource()
    .replace("alert(a)", "alert('function modified - ' + a)")
    .replace(/^function[^{]+{/i,"")  // remove everything up to and including the first curly bracket
    .replace(/}[^}]*$/i, "")  // remove last curly bracket and everything after

);

Instead of toSource() you could probably use toString() to get a string containing the function's declaration. Some calls to replace() to prepare the string for use with the Function Constructor and to modify the function's source.