function User(name){
    this.name=name;
    this.show=function(){
        console.log(this);
    }
}

let xj=new User("xj");
xj.show();//对象去调用的时候this指向当前对象     User {name: 'xj', show: ƒ}

//如果是当作普通函数调用,this指向是window
let xj1=xj.show;
xj1();//Window {window: Window, self: Window, document: document, name: '', location: Location, …}

// 严格模式下，this是undefined

//可以看this指向那一章