The [proposal](https://github.com/tc39/proposal-object-rest-spread) was finalized for ES2018. See `spread_in_object_literals` in MDN's browser-compat-data: https://github.com/mdn/browser-compat-data/blob/master/javascript/operators/spread.json#L191
The proposal was finalized for ES2018.
See
spread_in_object_literalsin MDN's browser-compat-data: https://github.com/mdn/browser-compat-data/blob/master/javascript/operators/spread.json#L191