43 lines
1.6 KiB
Markdown
43 lines
1.6 KiB
Markdown
### createEventHub
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Creates a pub/sub ([publish–subscribe](https://en.wikipedia.org/wiki/Publish%E2%80%93subscribe_pattern)) event hub with `emit`, `on`, and `off` methods.
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Instantiate a new `Map` object to allow any event type (including objects) to be the key, and also so `Object.prototype` property names are not resolved.
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For `emit`, resolve the array of handlers based on the `event` argument and then run
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each one with `Array.forEach()` by passing in the data as an argument.
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For `on`, create an array for the event if it does not yet exist, then use `Array.push()` to add the handler
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to the array.
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For `off`, use `Array.findIndex()` to find the index of the handler in the event array and remove it using `Array.splice()`.
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```js
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const createEventHub = () => ({
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hub: new Map(),
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emit(event, data) {
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(this.hub.get(event) || []).forEach(handler => handler(data));
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},
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on(event, handler) {
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if (!this.hub.get(event)) this.hub.set(event, []);
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this.hub.get(event).push(handler);
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},
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off(event, handler) {
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const i = (this.hub.get(event) || []).findIndex(h => h === handler);
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if (i > -1) this.hub.get(event).splice(i, 1);
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}
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});
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```
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```js
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const fn = data => console.log(data);
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const obj = {};
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const hub = createEventHub();
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hub.on('message', fn); // subscribe a handler to listen for 'message' events
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hub.on(obj, fn); // subscribe a handler to listen for the object
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hub.emit('message', 'hello!'); // console logs 'hello!'
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hub.emit(obj, 'hello!'); // console logs 'hello!'
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hub.off('message', fn); // unsubscribe our handler from 'message', the obj event will still work
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```
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