js中的this指向问题及解决方案

//this的指向问题简介
//改写成class
class obj{
    constructor(){
        this.name = "zxh";  //必须要有this，this为当前的对象
        this.age = 12;  
    }
    say(){
       console.log(this.name+" "+this.age);
    }
}


class animals{
    constructor(){
       this.name = "gou";
        this.age = 23;
    }
    says(say){
       setTimeout(function(){
            console.debug(this.name+" "+this.age+" "+say);  //这里的this指向存在问题，：undefined undefined hahah
       },100);
    }
}
var ss = new animals();
ss.says("hahah");


//解决这的bug问题
//1、第一种方式，将this修改为animals，因为当前的this定义时是在当前对象，但是使用是在窗体对象，也就是全局对象中，所以this指向的不同
class animals{
    constructor(){
       this.name = "gou";
        this.age = 23;
    }
    says(say){
       setTimeout(function(){
            console.debug(animals.name+" "+animals.age+" "+say);
       },100);
    }
}
var ss = new animals();
ss.says("hahah");


//2、第二种方式，通过将copy this 实现指针指向当前的对象
class animals{
    constructor(){
       this.name = "gou";
        this.age = 23;
    }
    says(say){
       let thisCopy = this;
       setTimeout(function(){
            console.debug(thisCopy.name+" "+thisCopy.age+" "+say);
       },100);
    }
}
var ss = new animals();
ss.says("hahah");


//3、第三种方式，通过bind(this)实现
class animals{
    constructor(){
       this.name = "gou";
        this.age = 23;
    }
    says(say){
       let thisCopy = this;
       setTimeout(function(){
            console.debug(this.name+" "+this.age+" "+say);
       }.bind(this),100);
    }
}
var ss = new animals();
ss.says("hahah");
//4、第四种，通过es6 arrow实现,因为箭头函数时定义函数时和执行函数时都是指向的当前对象
class animals{
    constructor(){
        this.name = "zxh";
        this.age = 21;
    }
    says(say){
        setTimeout(()=>{
            console.log(this.name+" "+this.age+" "+say);
        },100);
    }
}
var ss = new animals();
ss.says("hahah");