prompt - non-recursively replace built-in javascript functions -

i writing bookmarklets here , have questions related built-in javascript functions.

let's want replace built-in prompt function (not in bookmarklet). seems easy enough, there way call builtin prompt function within replacement?

prompt = function(message){     var tmp = prompt(message);     hook(tmp);     return tmp; } 

i couldn't scoping work out right; example yields infinite recursion.

also there way restore default behavior of builtin javascript function has been replaced (without hanging on reference).

(function () {     var old_prompt = prompt;     prompt = function (msg) {         var tmp = old_prompt(msg);         hook(tmp);         return tmp;     };     prompt.restore = function () { prompt = old_prompt; }     // analogous other functions want replace })(); 

wrapping in (self-executing) function ensures old_prompt doesn't leak outside. need expose something though. chose provide function doing restoring, convenience , perhaps, 1 say, future-proofing , encapsulation. long higher order functions refrain fiddling else's scope...

also, no, it's (i'd assume) not possible restore previous value of variable without reference (the old value), if value happened built-in. if possible, it'd pretty obscure trick - way works, let's stick it.

(credit func.restore goes martijn)