Why does a function declaration override non-writable properties of the global object?

Question

Setting a property descriptor like this:

Object.defineProperty(window, 'someFunction', {
    value: function() { alert('safe'); },
    writable: false,
    enumerable: false,
    configurable: false
});

...should, as far as I know, make the someFunction property of window non-writable. It works for function expressions as I expect, whether the function is directly assigned to the object property... ^fiddle

window.someFunction = function() { alert('boom!'); }
someFunction(); // safe

...or assigned to a global variable: ^fiddle

var someFunction = function() { alert('boom!'); }
someFunction(); // safe

However, it doesn't seem to work with function declarations : ^fiddle

function someFunction() { alert('boom!'); }
someFunction(); // boom!

Is this behavior intentional? What is the reasoning behind it? Is this documented anywhere? Or am I just making some kind of silly mistake?

---

By the way, I'm using Chromium 17 to test this. Strict mode doesn't seem to make any difference.

Answer 1

This is a bug (see Bug #115452) , which I also encountered when answering this question .

Compatibility check: Test case

• In Firefox 4+, it works fine.
• In Chrome 16, it works fine.
• In Chrome 17, it does not work.
• IE8- doesn't have Object.defineProperty , so it doesn't work
• In IE9, it does not work.
• In Safari 5, it does not work.