Make a method to map a Map to an Object

map_maps.js

Object.fromMap = function(m, f) {
    var r = {};
    f = f || ((x, y) => [x, y]);
    for (let [k, v] of m) {
        [k, v] = f(k, v);
        r[k] = v;
    }
    return r;
}