[univerio]

For JS, implement a Map data structure that is keyed by the value (not identity) of arbitrary objects.

[xiphias2]

After I implemented this and compared with just encoding the key with JSON, it turned out that JSON.stringify is so fast, that it's not really worth the effort.

[univerio]

Unfortunately JSON.stringify makes no guarantees about the order of keys in an Object, so that can break in subtle ways.

[xiphias2]

Aha, that's true. I wasn't using hash maps when I did this, but what you write makes sense.