mozilla/sweet.js — pull request #406 by r3m0t (2014-10-17 18:02:20+00:00)
Title: Allow op assignment

This lets an operator return an lvalue.

Previously,

i@a.b = 5 + 2;

would be parsed as

$left:"i" $right:"a.b = 5 + 2"

which doesn't match Javascript.