javascript - 无法扩展EventEmitter？

Question

我正在尝试创建一个自定义事件发射器。看来我无法替换 on 和 emit，如下所示。

• 我尝试将方法分配给其他变量并使用它们，然后删除原始变量(不起作用)
• 我尝试将 on 和 emit 分配给不同的方法，例如 onTest 和 emitTest(有效)

这是扩展 EventEmitter 的类:

import { EventEmitter } from 'events'

export default class MyEventEmitter extends EventEmitter {
  constructor () {
    super()
    this._on = this.on
    this._emit = this.emit
    delete this.on
    delete this.emit
  }
  on () {
    this._on.apply(this, Object.values(arguments))
  }
  emit () {
    this._emit.apply(this, Object.values(arguments))
  }
}

let event = new MyEventEmitter()

event.on('hi', () => console.log('meow'))

event.emit('hi')

这是堆栈:

$ babel-node ./src/event-store/my-event-emitter.js 
/Users/thomas/.nvm/versions/node/v5.10.0/lib/node_modules/babel-cli/node_modules/babel-polyfill/node_modules/core-js/modules/es7.object.values.js:0



RangeError: Maximum call stack size exceeded
    at Object.propertyIsEnumerable (native)
    at /Users/thomas/.nvm/versions/node/v5.10.0/lib/node_modules/babel-cli/node_modules/babel-polyfill/node_modules/core-js/modules/_object-to-array.js:12:32
    at values (/Users/thomas/.nvm/versions/node/v5.10.0/lib/node_modules/babel-cli/node_modules/babel-polyfill/node_modules/core-js/modules/es7.object.values.js:7:12)
    at MyEventEmitter.emit (my-event-emitter.js:15:28)
    at MyEventEmitter.emit (my-event-emitter.js:15:16)
    at MyEventEmitter.emit (my-event-emitter.js:15:16)
    at MyEventEmitter.emit (my-event-emitter.js:15:16)
    at MyEventEmitter.emit (my-event-emitter.js:15:16)
    at MyEventEmitter.emit (my-event-emitter.js:15:16)
    at MyEventEmitter.emit (my-event-emitter.js:15:16)

更新 1

也尝试过此操作并收到相同的错误:

import { EventEmitter } from 'events'

export default class MyEventEmitter extends EventEmitter {
  constructor () {
    super()
  }
  on () {
    this.on.apply(this, Object.values(arguments))
  }
  emit () {
    this.emit.apply(this, Object.values(arguments))
  }
}

let event = new MyEventEmitter()

event.on('hi', () => console.log('meow'))

event.emit('hi')

Answer 1

您尝试重新定义这些继承的方法最终会得到 this._emit === this.emit，这又会在调用中产生无限递归。

如果你想覆盖方法，你应该这样做。无需将它们重新分配给其他名称或尝试删除实例甚至没有的属性。

export default class MyEventEmitter extends EventEmitter {
  on(...args) {
    return super.on(...args)
  }
  emit(...args) {
    return super.emit(...args);
  }
}

_{(我认为那些 Object.values 调用毫无意义)}