JavaScript object functions and `this` when unbound and returned in expression/parens
The grouping operator does not destroy property references, which are provoking the method call.
This is explicitly mentioned in the spec:
NOTE: This algorithm does not apply GetValue to the result of evaluating
Expression
. The principal motivation for this is so that operators such asdelete
andtypeof
may be applied to parenthesised expressions.
In your lines 4 and 5, it's not the parenthesis but the operators (?:
and ||
) that de-reference the property and yield the "unbound" function.
foo.bar
here is an anonymous function.
It might make more sense if you split it up into different lines:
foo = {
bar: function() {
return this;
}
}
So, when you call foo.bar
, you're getting function() { return this; }
. On line two, you call that function directly (foo.bar()
), so it returns this
, the instance of the object (foo
).
On line three, you get the same result because you're not only asking for the anonymous function, but executing that function as well:
(foo.bar); // (function() { return this; }); A reference to the function
(foo.bar)(); // (function() { return this; })(); Actually calling the function
Because in the latter case, you're executing the function as you did in line two, the result is the same (foo
).
In lines four and five, however, as Bergi said, the operators you use dereference them from the function, which leaves you with a Window
object rather than foo
.