705795 - better control of js warning in strict.

Status: RESOLVED DUPLICATE of bug 1619177

(Core :: JavaScript Engine, defect)

Description

[Irakli Gozalishvili [:irakli] [:gozala] [@gozala]]

In jetpack we set 'javascript.options.strict' pref to 'true' when running tests / debugging to identify code that is poorly written, or prone to cause logic errors. 

Arguably "reference to undefined property" warnings are useless, they prevent us from using:

1. Destructuring assignments:

Instead of writing:

let { a, b } = object;
if (a && b) // ...   

we end up with

let a = a in object && object.a;
let b = b in object && object.b;
if (a && b) // ...

2. Concise property comparison:

if (a.foo === b.foo) // ...

we end up with

if ('foo' in a ? ('foo' in b && foo.a === foo.b) || !b.foo : !('foo' in b)) //..

It would be very helpful to have more granular control of strict warnings for example a pref to disable / enable  'reference to undefined property' warnings.

Comment 1

[Kyle Huey (Exited; not receiving bugmail, old account, do not use)]

Core::Jemalloc is definitely not the right place for this.

Comment 2

[Myk Melez [:myk] [@mykmelez]]

I particularly notice this when using destructuring assignment as a poor man's named parameters:

    > function foo({ bar }) {}; foo({});

    Warning: reference to undefined property "bar"
    Source file: javascript:%20function%20foo({%20bar%20})%20{};%20foo({});
    Line: 1

I would rather not be warned in these cases, especially since I can't distinguish between optional and required parameters (although if I could, then I'd want the JS engine to generate an exception rather than a warning if a required one was missing).

Comment 3

[[github robot]]

Commit pushed to https://github.com/mozilla/addon-sdk

https://github.com/mozilla/addon-sdk/commit/207d37a4271f504cf4f496fad5befdbb00e6747e
always set "principal" to work around bug 705795