手写一个EventBus(发布订阅模式)

Author：五毛
发布时间：December 8, 2020
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1071 words
Categories：个人笔记

实际上EventBus就是一个发布订阅模式，简单实现如下

```java
class EventBus {
  constructor() {
    this.onList = []
  }
  on(name, fn) {   //订阅事件
    this.onList.push({
      name,
      fn,
      isOnce: false
    })
  }
  emit(name, targetVal) {  //发布事件
    this.onList.forEach((obj, index) => {
      if (obj.name === name) {
        obj.fn(targetVal)
        if (obj.isOnce) this.onList.splice(index, 1)
      }
    })
  }
  once(name, fn) {
    this.onList.push({
      name,
      fn,
      isOnce: true
    })
  }
  off(name) {
    const index = this.onList.findIndex(val => val.name === name)
    if (index > -1) this.onList.splice(index, 1)
  }

}

module.exports = EventBus
```

使用

```javascript
const EventBus = require('./EventBus.js')

const bus = new EventBus()
bus.on('log', value => {
  console.log('触发' + value)
})

bus.once('onceLog', value => {
  console.log('触发一次' + value)
})
bus.off('log')
bus.emit('log', 'emit的值')
bus.emit('log', 'emit的值')
bus.emit('onceLog', 'onceLog的值')
bus.emit('onceLog', 'onceLog的值')

```

Last modification：December 8, 2020