JS does indeed allow mapping arbitrary objects to keys. However, it is the memory address of the object that is hashed, not the semantic value. So, for example, if you do:

    objects = {}
    items1 = ["a", "b"]
    items2 = ["a", "b"]
    objects[items1] = 1
    objects[items2] = 2

then objects[items1] will return 1, and objects[items2] will return 2, but objects[items1] !== objects[items2].

EDIT: Sorry, this only works for dictionaries that are Maps, not Objects! See the responses. My fuzzing about in the console led me astray; you should start with `objects = new Map()` instead of `objects = {}`.