var myMap = new Map();

var aKey = Symbol('skeleton');
myMap.set('name', 'Nick');
myMap.set('age', 29);
myMap.set(aKey, ()=>'secret password');

console.log(myMap);
//Map(3) {"name" => "Nick", "age" => 29, ()=> 'secret password'}
console.log(myMap.get('skeleton'));
//undefined
console.log(myMap.get(aKey)());
//secret password

console.log(myMap.has('name'));
//true

console.log(myMap.size);
//3