What's the difference between ES6 Map and WeakMap?

Question

Looking this and this MDN pages it seems like the only difference between Maps and WeakMaps is a missing \"size\" property for WeakMaps. But is this true? What\'s the differ

Answer 1

From Javascript.info

Map -- If we use an object as the key in a regular Map, then while the Map exists, that object exists as well. It occupies memory and may not be garbage collected.

let john = { name: "John" };
let array = [ john ];
john = null; // overwrite the reference

// john is stored inside the array, so it won't be garbage-collected
// we can get it as array[0]

Similar to that, if we use an object as the key in a regular Map, then while the Map exists, that object exists as well. It occupies memory and may not be garbage collected

let john = { name: "John" };
let map = new Map();
map.set(john, "...");
john = null; // overwrite the reference

// john is stored inside the map,
// we can get it by using map.keys()

WeakMap -- Now, if we use an object as the key in it, and there are no other references to that object – it will be removed from memory (and from the map) automatically.

let john = { name: "John" };
let weakMap = new WeakMap();
weakMap.set(john, "...");
john = null; // overwrite the reference

// john is removed from memory!