JS: Map.prototype.forEach

New in ES2015.

• map_obj.forEach(f)
• map_obj.forEach(f, thisArg)

Apply function f to all entries in map map_obj in the order the entries are inserted. Does not modify the map object. Return undefined.

If thisArg is given, it will be used as this value of f. If it is not given, undefined is used.

The function f is passed 3 arguments: value, key, map_object.

Note the order of the value/key.

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

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

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

See also: JS: Iterate Over Map Object