1300416 - Default destructuring logs a "reference to undefined property" strict warning

Status: RESOLVED DUPLICATE of bug 1455179

(Core :: JavaScript Engine, defect, P3)

Description

[Lina Butler [:lina]]

Using default destructuring in an xpcshell test (or with `javascript.options.strict` enabled) prints a warning if the object on the right-hand side doesn't have the property. For example, the following:

    function acceptsDefaults(options = {}) {
      let { sprinkles = "chocolate" } = options;
      return sprinkles;
    }
    
    acceptsDefaults();

...Prints "JavaScript Warning: ReferenceError: reference to undefined property options.sprinkles" to the console.

This breaks tests that call into a JSM with a function like that, then listen for console output (http://searchfox.org/mozilla-central/rev/3582398bc9db5a83e25c2a8299cc780a52ad7ca8/browser/components/places/tests/unit/head_bookmarks.js#71-98, for instance).

While we can (and probably should) fix the test to filter out logged JS warnings, I'm wondering if the warning is needed for this case at all. ISTM code that provides a default value for destructuring expects that the property not be present.