JS maps already have a well defined way that they do key equality: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map#key_equa

JS maps already have a well defined way that they do key equality: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map#key_equality https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe... It's basically just strict equality (===), except NaN === NaN is false, while they're considered equal for map keys. So in your example, you'd have 2 entries, since {} !== {}. It sounds like they're going to implement `groupByToMap` as well as `groupBy`, and I assume `groupByToMap` will just use the normal map key equality rules, and I guess the "first" key matching that equality will be used for the grouping.