A question about uninitialized variables

[NWU-NISL]

Version

chakra-1_11_22

Test case

var h = function f(a0 = function () {
  a2;
}(), a2) {
};
h();

Execution steps

./ChakraCore/out/Debug/ch testcase.js

Output

Expected behavior

ReferenceError: can't access lexical declaration `a2' before initialization

Description

When executing this test case, a2 is not initialized before the call, other engines (such as v8, spiderMonkey, JavaScriptCore, etc.) threw a ReferenceError, but chakra did not do so. Is this a different implementation of chakra?

[ppenzin]

The symbol is defined in the second argument, but used in the first. I need to research the scoping rules a bit more, but if the arguments have to be evaluated left to right, this would be a bug.

[pleath]

The other engines are right. I can imagine a couple of possible root causes: a2 isn't being initialized prior to the evaluation of a0 in a way that supports the use-before-declaration check, or the reference to a2 isn't being properly bound to the parameter.

[ppenzin]

I am going to cautiously add some labels inviting contributions, I am still on the fence whether this should be a beginner issue.

[pleath]

Hm. I wouldn't necessarily call it a beginner issue. It likely has to do with the binding algorithm in the parser, which isn't trivial.

[ppenzin]

OK, let's keep this one off "good first issue" list for now.