In Node.js's REPL (tested in SpiderMonkey as well) the sequence
var foo = null;
(foo) = "bar";
is valid, with foo subsequently equal to "bar" as opposed to null.
This seems counterintuitive because one would think the parenthesis would at least dereference bar and throw Invalid left-hand side in assignment`.
Understandably, when you do anything interesting it does fail in aforementioned way.
(foo, bar) = 4
(true ? bar : foo) = 4
According to ECMA-262 on LeftHandExpressions (so far as I can interpret) are no valid non-terminals that would lead to a parenthetical being accepted.
Is there something I'm not seeing?