Defaultdict Packages

collections.py for JavaScript

Dictionary-like object with a handler for missing keys

An extension of Map that auto-initializes new values with empty collections and auto-removes empty collections being set

Python's collections library for JavaScript

Helpful collections shamelessly copied from Python and ported to JS: orhttps://docs.python.org/2/library/collections.html#module-collections

Python's collections library for JavaScript

Simple solution to this problem: "TypeError: Cannot set property 'x' of undefined"

A Map subclass that automatically adds missing values