I wonder if groupBy should have had some sort of into argument. Otherwise, we may end up with four groupBy methods. groupBy, groupByToMap, groupByToWeakMap and groupByToRecord (should records land).

Edit: this has already been discussed https://github.com/tc39/proposal-array-grouping/issues/3

updated the post with groupByToMap, Thanks for pointing that out.

Ah fair enough!