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46 lines
1,023 B
Markdown
46 lines
1,023 B
Markdown
---
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date: 2020-10-12
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id: e06279b3-4488-40b1-b822-fca19b47089a
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title: JavaScript WeakMaps
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---
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# Introduction
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A WeakMap is a [Map](20201012093745-javascript_maps) that doesn’t
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prevent its keys from being garbage-collected. That means that you can
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associate data with [objects](20200826201605-objects) without having to
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worry about memory leaks.
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# Example
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``` javascript
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//----- Manage listeners
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const _objToListeners = new WeakMap();
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function addListener(obj, listener) {
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if (! _objToListeners.has(obj)) {
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_objToListeners.set(obj, new Set());
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}
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_objToListeners.get(obj).add(listener);
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}
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function triggerListeners(obj) {
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const listeners = _objToListeners.get(obj);
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if (listeners) {
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for (const listener of listeners) {
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listener();
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}
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}
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}
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//----- Example: attach listeners to an object
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const obj = {};
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addListener(obj, () => console.log('hello'));
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addListener(obj, () => console.log('world'));
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//----- Example: trigger listeners
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triggerListeners(obj);
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```
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