840400 - Add an IsObject(v) method to self-hosted Utilities.js

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Jeff Walden [:Waldo]]

Attachment: Patch

Checking whether a value is an object is non-trivial on multiple levels.  And judging by even a subset of the patches in bug 769872, that test is going to end up being performed in a lot of places, even if many are assertions.  Abstractions to the rescue!

Comment 1

[Norbert Lindenberg]

Comment on attachment 712764 [details] [diff] [review]
Patch

Review of attachment 712764 [details] [diff] [review]:
-----------------------------------------------------------------

Good idea.

::: js/src/builtin/Utilities.js
@@ +107,4 @@
>  }
>  
>  
> +/********** Abstract operations defined in ECMAScript Language Specification **********/

You mean "Common operations not defined..."?

@@ +109,5 @@
>  
> +/********** Abstract operations defined in ECMAScript Language Specification **********/
> +
> +
> +/* Spec: ECMAScript Language Specification, 5.1 edition, 8.12.6 and 11.8.7 */

These sections don't say anything relevant to IsObject. 11.4.3 is relevant, but part of the behavior depends on a non-standard SpiderMonkey extension.

@@ +114,5 @@
> +function IsObject(v) {
> +    // Watch out for |typeof null === "object"| as the most obvious pitfall.
> +    // But also be careful of SpiderMonkey's objects that emulate undefined
> +    // (i.e. |document.all|), which have bogus |typeof| behavior.  Detect
> +    // these objects using strict equality, which said bogosity doesn't affect.

There's some loss of information compared to my previous comment, but maybe that's OK.

Comment 2

[Jeff Walden [:Waldo]]

Attachment: With a non-copied comment

Oops, I should have updated the comments when I copy-pasted from earlier.

Comment 3

[Jeff Walden [:Waldo]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/6be86adf9bf2

Comment 4

[Ed Morley [:emorley]]

https://hg.mozilla.org/mozilla-central/rev/6be86adf9bf2