Created attachment 265448 [details] [TEST] Set Existence Benchmark * SUMMARY Set existence with numeric values slower than numeric object property existence. In Web Inspector we were converting a bunch of uses of "Object as Set" and "Object as Map" to Set/Map objects. I wrote a small benchmark to compare possible performance differences. Existence checks for large dense Sets with primitives is worse than existence checks in large dense Objects. object[number] - 17ms number in object - 84ms set.has(number) - 622ms For numeric keys object was significantly faster than Set. For other key types the effect was not as large. See attached test case. * NOTES - Not sure how realistic the test is for real world code. Especially given Set's major advantage is non-primitive keys.