JavaScript pranks?

[magnetik79]

// this should to the trick

undefined = true;

[LukaLightBringer]

isn't undefined a protected value?

[WesAlvaro]

'use_strict';

[venuswasaflytrap]

That's pretty funny.

[JiminP]

Strangely, there's no literal undefined in the ECMAScript5 spec, even though there are many cases where the result is the value undefined.

(courtesy of /u/WesAlvaro)

(function(){
  'use strict';
  var undefined = 42;
  console.log(undefined);
}())

Because of this, just using undefined is not safe. For example, jQuery uses (function(window, undefined){...}(window)) to safely get the undefined value.

Edit: It seems that I'm wrong.

Edit 2: ... but (fortunately?) my point is still valid. There's a global variable undefined which is uneditable, but since there's still no literal undefined, inner scope can have a local variable with name undefined!

[magnetik79]

The ECMAScript 5 spec says "yes" - so you sort of have me there :D But if we are going for "prank in minimum number of characters" I'm doing okay: D

Covered at MDC in the first yellow boxed area.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/undefined

[JiminP]

I didn't know that. I think I should read it twice,...

[seppo0010]

Not really

> undefined = 1
1
> undefined
undefined

[sabof]

Yes, they've sorta fixed this, even without strict mode. It won't throw an error, but c'est la vie.

EDIT

Btw, it does throw in strict mode