Events

events.js

class MyEvents {
	constructor () {
		this.events = {} //存储事件监听函数
		this.maxListeners = 10 //一种函数类型，最大监听函数数量
	}
	
	setMaxListeners (maxNum) {
		this.maxListeners = maxNum
	}
	
	getMaxListeners () {
		return this.maxListeners
	}
	
	listeners (event) {
		return this.events[event]
	}
	
	addListener (type, listener) {
		if (this.events[type]) {
			if (this.maxListeners != 0 && this.events[type].length > this.maxListeners) {
				return console.error(`该${type}事件类型的listteners超出限制，使用emitter.setMaxListeners() 来增加添加事件监听数量。`)
			}
			this.events[type].push(listener)
		} else {
			this.events[type] = [listener]
		}
	}
	
	once (type, listener) {
		//执行后立即销毁
		let wrapper = (...rest) => {
			listener.apply(this, rest)
			this.removeListener(type, wrapper)
		}
		this.addListener(type, wrapper)
	}
	
	removeListener (type, listener) {
		if (this.events[type]) {
			this.events[type] = this.events[type].filter(ev => {
				ev != listener
			})
			//抛弃掉等于listener的
		}
	}
	
	removeAllListener (type) {
		delete this.events[type]
	}
	
	emit (type, ...rest) {
		this.events[type] && this.events[type].forEach(listener => {
			listener.apply(this, rest)
		})
	}
}

MyEvents.prototype.on = MyEvents.prototype.addListener
module.exports =  MyEvents

作者：happyGloria
链接：https://juejin.im/post/5a6ebc056fb9a01ca072172b
来源：掘金
著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。

var EventTarget = function() {
  this.listeners = {};
};

EventTarget.prototype.listeners = null;
EventTarget.prototype.addEventListener = function(type, callback) {
  if (!(type in this.listeners)) {
    this.listeners[type] = [];
  }
  this.listeners[type].push(callback);
};

EventTarget.prototype.removeEventListener = function(type, callback) {
  if (!(type in this.listeners)) {
    return;
  }
  var stack = this.listeners[type];
  for (var i = 0, l = stack.length; i < l; i++) {
    if (stack[i] === callback){
      stack.splice(i, 1);
      return;
    }
  }
};

EventTarget.prototype.dispatchEvent = function(event) {
  if (!(event.type in this.listeners)) {
    return true;
  }
  var stack = this.listeners[event.type];

  for (var i = 0, l = stack.length; i < l; i++) {
    stack[i].call(this, event);
  }
  return !event.defaultPrevented;
};

• Simple implementation of EventTarget