var roles = new Map([ 
   ['r1', 'User'], 
   ['r2', 'Guest'], 
   ['r3', 'Admin'], 
]);

console.log(typeof(roles)); //object
console.log(roles);
		

var m = new Map();

// set
m.set("name", "Lin");
m.set("age", 39);

// get
console.log(m.get("name"));

// size
console.log(m.size);

// has
console.log(m.has("name"));
		

var m = new Map();

// set chains
m.set("name", "Lin").set("age", 39);

console.log(m)
		

var roles = new Map([ 
   ['r1', 'User'], 
   ['r2', 'Guest'], 
   ['r3', 'Admin'], 
]);

// delete
console.log(roles.delete('r1')); // true
console.log(roles);

// entries
var itr = roles.entries(); // iterator object

for (const [key, value] of itr) {
  console.log(key, value);
}

// forEach
roles.forEach((value, key) => console.log(value));

// keys
var keys = roles.keys(); // iterator object

for (const key of keys)
	console.log(roles.get(key));

// values
var values = roles.values(); // iterator object

for (const value of values)
	console.log(value);

// clear
roles.clear();
		

Its keys must be objects

Keys in a weak map can be Garbage collected. Garbage collection is a process of clearing the memory occupied by unreferenced objects in a program

A weak map cannot be iterated or cleared

let weakMap = new WeakMap();

let obj = {};
let obj2 = {name: 'Lin'};
weakMap.set(obj, 'hello');
weakMap.set(obj2, 39);

console.log(weakMap);
console.log(weakMap.has(obj));
console.log(weakMap.get(obj2));