Why does a function declaration override non-writable properties of the global object?
-
13-12-2019 - |
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.
Solution
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.
Licensed under: CC-BY-SA with attribution
Not affiliated with StackOverflow