What is the purpose of the WeakMap object?

I recommend reading the question on Map first. The type WeakMap works exactly like Map , with the following main differences:

The last one is in bold because it is the reason why WeakMap exists. A "weak reference" in this context means that the use of a given object as a key in a WeakMap does not count from the garbage collector's point of view. If there is no other reference to an object used as a key in a WeakMap , the value corresponding to that key in WeakMap is released to be collected by the garbage collector .

How does the WeakMap object work?

WeakMap is an object of Javascript that provides an object dictionary, that is, an object that stores data in the key / value format.

As a dictionary, it works based on a key, that is, for include / retrieve / delete operations is using a key to identify the object.

Here is an example of creating a dictionary and the basic operations:

var dic = new WeakMap()

//chaves
var chaveA = { chave: 'A' };
var chaveB = { chave: 'B' };
var chaveC = { chave: 'C' };

// adicionando objetos
dic.set(chaveA, 1);
dic.set(chaveB, "dois");
dic.set(chaveC, new Date(2018,06,13));

// verificando objetos
console.log("existe objeto 'A':" + dic.has(chaveA));

// recuperando
console.log("valor do objeto 'A':" + dic.get(chaveA));
console.log("valor do objeto 'B':" + dic.get(chaveB));
console.log("valor do objeto 'C':" + dic.get(chaveC));

// excluindo
dic.delete(chaveA);
console.log("existe objeto 'A':" + dic.has(chaveA));

What is the difference between it and an Object (which is the most common in Javascript)?

Key differences:

• does not have a method to retrieve an object, as WeakMap has get() ;
• does not have a method to assign values like set() of WeakMap, it is necessary to use the = operator;
• does not have a method to clean properties like clear() of WeakMap;

What is the difference between WeakMap and Map?

Key differences:

• Map is iterable and therefore supports forEach , since WeakMap does not.
• The key of a Map object can be any object ( string , number , etc), while WeakMap must be Object .

Which browsers can I use?

According to developer.mozila.org on 7/13/2018 the compatibility is:

Chrome  Firefox     Internet Explorer   Opera           Safari
36      6.0 (6.0)   11                  Não suportado   Não suportado

developer.mozilla.org