Assignment with invalid LHS does not throw SyntaxError

[AnirudhKonduru]

Assignments with invalid left-hand side(1=2) return the value of the right-hand side(2) instead of throwing SyntaxError.

To Reproduce

This JavaScript code reproduces the issue:

1=2 # should throw SyntaxError

-->

Expected behavior

The spec for the expected behaviour can be found in the ECMAScript specification.

[Lan2u]

Fixed by #559