1040976 - Add an option to enable to extraWarnings flag in the JS engine for a web page

Status: NEW

(DevTools :: General, defect, P3)

Description

[Bill McCloskey [inactive unless it's an emergency] (:billm)]

The extraWarnings flag in the JS engine generates warnings when you do things that are legal in JS, but probably errors. The most useful example is accessing properties that don't exist. Right now this option is enabled only for chrome code, and only in debug builds. I think it's really great for tracking down JS bugs.

Pretty soon we'll be able to enable this option on a per-compartment bases (bug 940305). It would be great if devtools exposed a checkbox or something so that developers could get these warnings if they wanted. I think it would be a nice competitive advantage. As a web developer, the lack of these warnings was always my biggest complaint about JS.

Comment 1

[Joe Walker [:jwalker]]

Does this mean that content will warn on the following:

    var t = {};
    if (t.foo == null) {
      // do something
    }

That's not too common in moz code, but it's much more common on the web. IIRC it's part of the crockford style guide.

Comment 2

[Bill McCloskey [inactive unless it's an emergency] (:billm)]

(In reply to Joe Walker [:jwalker] from comment #1)
> Does this mean that content will warn on the following:
> 
>     var t = {};
>     if (t.foo == null) {
>       // do something
>     }
> 
> That's not too common in moz code, but it's much more common on the web.
> IIRC it's part of the crockford style guide.

No, it knows about that pattern and doesn't warn about it.