Comments on: More ES5 backwards-incompatible changes: the global properties undefined, NaN, and Infinity are now immutable

By: Jeff

Jeff — Fri, 15 Jan 2010 20:52:40 +0000

If you have warnings enabled via javascript.options.strict, then yes, you’ll get a warning.

By: Where’s Walden? » More ES5 backwards-incompatible changes: regular expressions now evaluate to a new object, not the same object, each time they’re encountered

Fri, 15 Jan 2010 20:50:48 +0000

[...] as with my previous post, we doubt this change will affect many scripts (in this case, except for the better). The fact that [...]

By: Benjamin Stover

Benjamin Stover — Fri, 15 Jan 2010 17:39:19 +0000

Hopefully a warning will be generated when Firefox does nothing in non-strict mode?

By: voracity

voracity — Wed, 13 Jan 2010 06:11:50 +0000

Sure, that’s fine. ‘undefined’ is such a primitive and crucial concept, that there’s no justification I can think of (or even imagine) for overloading it. (At least, not in this context.)

By: Justin Dolske

Justin Dolske — Wed, 13 Jan 2010 06:04:23 +0000

Cruel interview question: blackbox debugging of a subtle bug caused by |undefined = “undefined”|.

By: Jeff

Jeff — Wed, 13 Jan 2010 03:55:14 +0000

The only changes made were to the properties of the global object. This example creates a local variable whose name means that it happens to shadow the name of a global property. That’s perfectly acceptable as far as both ES3 and ES5 go, so your example should print “value: 17″.

None of that, however, changes the fact that you shouldn’t be doing this! This is incredibly, incredibly poor style likely to confuse anyone who reads your code. (This is another thing that making these names keywords would have “fixed” by breaking the code, incidentally.)

By: voracity

voracity — Wed, 13 Jan 2010 03:45:18 +0000

What will:

function foo() {
  var undefined = 17;
  print("value: " + undefined);
};
foo();

do?