JS: Map.prototype.forEach

(new in JS: ECMAScript 2015)

mapObj.forEach(f)

• Apply function f to all entries in map mapObj in the order the entries are inserted. Does not modify the map object.
• Return undefined.
• f is passed 3 arguments: value, key, mapObj. Note the order in parameter is value first.

const mm = new Map([["a", 1], ["b", 2]]);

const rr = mm.forEach((v, k) => {
  console.log(v, k);
});
// 1 'a'
// 2 'b'

// returns undefined
console.log(rr === undefined);

mapObj.forEach(f, thisArg)

Use thisArg for this (binding) of f. If it is not given, undefined is used.