• node事件模塊使用方法

let EventEmitter=require('events');
let {inherits}=require('util');
function Girl() {
    
}
inherits(Girl,EventEmitter);
let girl=new Girl();
girl.on('失戀',cry);
girl.emit('失戀');

function cry() {
    console.log('哭')
}

class EventEmitter{
    constructor(){
        this._events={};
    }
    on(eventName,callback){
        if(!this._events[eventName]){
            this._events[eventName]=[callback];
        }else {
            this._events[eventName].push(callback);
        }
    }
    once(eventName,callback){
        let fn=()=>{//綁定的是fn,執(zhí)行的時候會觸發(fā)fn函數(shù)
          callback();//fn函數(shù)中調(diào)用原有的callback
            this.removeListener(eventName,fn);//刪除fn，再次執(zhí)行時只會執(zhí)行一次
        };
        this.on(eventName,fn);//1，先綁定，callback調(diào)用后再解綁,2要在callback中刪除綁定

    }
    removeListener(eventName,callback){
        if(this._events[eventName]){
            this._events[eventName]=this._events[eventName].filter(cb=>cb!=callback);
        }
    }
    emit(eventName){
        if(this._events[eventName]){
            this._events[eventName].forEach(cb=>cb());
        }
    }
}
let ev=new EventEmitter();

let cry=()=>{console.log('cry')};
ev.once('失戀',cry);
ev.on('失戀',cry);
ev.removeListener('失戀',cry);
ev.emit('失戀');