Comments on: Does JavaScript undefined Equals undefined?

By: xianyu

xianyu — Sat, 22 Oct 2011 16:55:50 +0000

When it runs in firebug console, it alert false. Use console.log(a), it return [a, ,a …]. Here a means the HTMLLinkElements collections

Stoimen — Fri, 21 Oct 2011 12:30:29 +0000

Actually you're right somehow! When I test it with the Firebug console ...

var a;
var b = undefined;
alert(a === b);

... it strangely returns true. But within a <script> tag ...

<script>
var a;
var b = undefined;
alert(a === b);
</script>

is FALSE. Isn't it weird?

Stoimen — Fri, 21 Oct 2011 12:23:19 +0000

It’s great that Chrome returns true, but if that’s not the case at the other “modern” browsers, then what?

Jason Mulligan — Fri, 21 Oct 2011 11:42:44 +0000

Stoimen — Fri, 21 Oct 2011 11:40:19 +0000

@Jason Mulligan – wrong, again “false”

Jason Mulligan — Fri, 21 Oct 2011 11:38:26 +0000

Triple equal operator for strict comparison.

a === b; // true