defaultDict.js

/* Kinda like Python's defaultdict, but for JS*/
function defDict(type) {
    var dict = {};
    return {
        get: function (key) {
        if (!dict[key]) {
            dict[key] = type.constructor();
        }
        return dict[key];
        },
        dict: dict
    };
}

/* Usage*/
var a = defDict([]);
a.get('a').push(1);
a.get('a').push(2);
a.get('b').push(3);
console.log(a.dict)

This was super helpful. Thanks!