50 lines
1.9 KiB
Markdown
50 lines
1.9 KiB
Markdown
---
|
||
title: createEventHub
|
||
tags: browser,event,advanced
|
||
---
|
||
|
||
Creates a pub/sub ([publish–subscribe](https://en.wikipedia.org/wiki/Publish%E2%80%93subscribe_pattern)) event hub with `emit`, `on`, and `off` methods.
|
||
|
||
- Use `Object.create(null)` to create an empty `hub` object that does not inherit properties from `Object.prototype`.
|
||
- For `emit`, resolve the array of handlers based on the `event` argument and then run each one with `Array.prototype.forEach()` by passing in the data as an argument.
|
||
- For `on`, create an array for the event if it does not yet exist, then use `Array.prototype.push()` to add the handler
|
||
- to the array.
|
||
- For `off`, use `Array.prototype.findIndex()` to find the index of the handler in the event array and remove it using `Array.prototype.splice()`.
|
||
|
||
```js
|
||
const createEventHub = () => ({
|
||
hub: Object.create(null),
|
||
emit(event, data) {
|
||
(this.hub[event] || []).forEach(handler => handler(data));
|
||
},
|
||
on(event, handler) {
|
||
if (!this.hub[event]) this.hub[event] = [];
|
||
this.hub[event].push(handler);
|
||
},
|
||
off(event, handler) {
|
||
const i = (this.hub[event] || []).findIndex(h => h === handler);
|
||
if (i > -1) this.hub[event].splice(i, 1);
|
||
if (this.hub[event].length === 0) delete this.hub[event];
|
||
}
|
||
});
|
||
```
|
||
|
||
```js
|
||
const handler = data => console.log(data);
|
||
const hub = createEventHub();
|
||
let increment = 0;
|
||
|
||
// Subscribe: listen for different types of events
|
||
hub.on('message', handler);
|
||
hub.on('message', () => console.log('Message event fired'));
|
||
hub.on('increment', () => increment++);
|
||
|
||
// Publish: emit events to invoke all handlers subscribed to them, passing the data to them as an argument
|
||
hub.emit('message', 'hello world'); // logs 'hello world' and 'Message event fired'
|
||
hub.emit('message', { hello: 'world' }); // logs the object and 'Message event fired'
|
||
hub.emit('increment'); // `increment` variable is now 1
|
||
|
||
// Unsubscribe: stop a specific handler from listening to the 'message' event
|
||
hub.off('message', handler);
|
||
```
|