arity binding decorator for javascript

gistfile1.js

function arity_decorator(fun) {
    function wrapped() {
        if(arguments.length != fun.length)
            throw new Error("Y U NO USE RIGHT?!")
        fun.apply(this, arguments);
    }
    return wrapped;
}

function foo(x, y) {
    console.log('X:' + x);
    console.log('Y:' + y);
}

foo = arity_decorator(foo);


/*
 * This is what it looks like to use it. Notice an error is thrown when the
 * wrong Arity is used.
 */

> function arity_decorator(fun) {
...     function wrapped() {
...         if(arguments.length != fun.length)
...             throw new Error("Y U NO USE RIGHT?!")
...         fun.apply(this, arguments);
...     }
...     return wrapped;
... }
> 
> 
> function foo(x, y) {
...     console.log('X:' + x);
...     console.log('Y:' + y);
... }
> 
> 
> foo = arity_decorator(foo);
[Function: wrapped]
> 
> foo()
Error: Y U NO USE RIGHT?!
    at wrapped ([object Context]:4:7)
    at [object Context]:1:1
    at Interface.<anonymous> (repl.js:171:22)
    at Interface.emit (events.js:64:17)
    at Interface._onLine (readline.js:153:10)
    at Interface._line (readline.js:408:8)
    at Interface._ttyWrite (readline.js:585:14)
    at ReadStream.<anonymous> (readline.js:73:12)
    at ReadStream.emit (events.js:81:20)
    at ReadStream._emitKey (tty_posix.js:307:10)

> foo(3,4)
X:3
Y:4

> foo(3,4,5)
Error: Y U NO USE RIGHT?!
    at wrapped ([object Context]:4:7)
    at [object Context]:1:1
    at Interface.<anonymous> (repl.js:171:22)
    at Interface.emit (events.js:64:17)
    at Interface._onLine (readline.js:153:10)
    at Interface._line (readline.js:408:8)
    at Interface._ttyWrite (readline.js:585:14)
    at ReadStream.<anonymous> (readline.js:73:12)
    at ReadStream.emit (events.js:81:20)
    at ReadStream._emitKey (tty_posix.js:307:10)
>