Are parentheses ignored if they only contain a property accessor?

Question

Given the following code, why doesn't (obj.foo)() receive window as this? It seems to me like the parentheses are ignored, rather than treated as an expression that evaluates to foo?

window.bar = 'window';
const obj = { bar: 'obj' };

obj.foo = function() {
  console.log(`Called through ${this.bar}`);
}

obj.foo(); // Called through obj

(obj.foo)(); // Called through obj - Why?

(0, obj.foo)(); // Called through window

(true && obj.foo)(); // Called through window

Here you can probably find a good explanation of the same behavior: https://stackoverflow.com/questions/36076794/does-the-comma-operator-influence-the-execution-context-in-javascript/36077031#36077031 — Alberto Chiesa, Nov 21 '19 at 08:22
@A.Chiesa - I didn't realize from your comment that that's a good dupetarget for this. Marked it. — T.J. Crowder, Nov 21 '19 at 08:25
@T.J.Crowder Well, the wording is quite different, even if the concepts are exactly the same. I think I'm going to update the answer with the _Reference_ explanation — Alberto Chiesa, Nov 21 '19 at 08:28

score 2 · Accepted Answer · answered Nov 21 '19 at 08:24

They're not ignored, but the result of (obj.foo) is the same Reference (specification term) as the result of obj.foo (see this section in the spec). So the property accessor has the same information to work with to get the object and property and to use that object as this.

score 1 · Answer 2 · answered Nov 21 '19 at 08:24

1

Cause obj.foo evaluates to a Reference that contains obj and "foo". When you [[Call]] the reference, both obj and foo are known as part of the Reference.

Most operators (including the comma operator) evaluate the Reference to a value.

answered Nov 21 '19 at 08:24

Jonas Wilms

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Are parentheses ignored if they only contain a property accessor?

2 Answers2