JavaScript WeakMaps

Introduction

A WeakMap is a Map that doesn’t prevent its keys from being garbage-collected. That means that you can associate data with objects without having to worry about memory leaks.

Example

//----- Manage listeners
 
const _objToListeners = new WeakMap();
 
function addListener(obj, listener) {
    if (! _objToListeners.has(obj)) {
        _objToListeners.set(obj, new Set());
    }
    _objToListeners.get(obj).add(listener);
}
 
function triggerListeners(obj) {
    const listeners = _objToListeners.get(obj);
    if (listeners) {
        for (const listener of listeners) {
            listener();
        }
    }
}
 
//----- Example: attach listeners to an object
 
const obj = {};
addListener(obj, () => console.log('hello'));
addListener(obj, () => console.log('world'));
 
//----- Example: trigger listeners
 
triggerListeners(obj);