bad_js_dont_do_this.txt

You are looking for the built-in `dict` data-type. However, keys must be *hashable* objects. 
Python prevents you from shooting yourself in the foot by using a mutable object as a key 
(although, you can implement your own data-type which is mutable and hashable, but you *shouldn't*). 
Note, consider the following JS code:

    > m1 = new Map([['a', 1]])
    Map { 'a' => 1 }
    > m2 = new Map()
    Map {}
    > m2.set(m1, 3)
    Map { Map { 'a' => 1 } => 3 }
    > m2.get(m1)
    3

Seems ok at first blush. Ideally, though, you want keys with the *same value* to retrieve the corresponding 
value from the map. So...

    > m2.get(new Map([['a',1]]))
    undefined

So really, how useful is this map?

What JS does under the hood is hash by *identity* in this case.