6 this指向

1-普通函数、全局作用域、定时器

##this指向window
        //普通函数中的this  指向window
        function go(){
            console.log(this);
        }
        go();//window
 //定时器
 <button id="btn">btn</button>
    <script>
        var btn = document.getElementById("btn");
        btn.onclick = function(){
            setTimeout(function(){
                console.log(this);//window
            },500)
        }
    </script>

2-方法

#this指向调用它的对象
<script>
        var name = "window"
        var obj = {
            name:"javascript",
            sayName(){
                console.log(this.name);
            },
            wait(){
                console.log(this.name);//javascript
                setTimeout(function(){
                    console.log(this.name);
                })
            },
            delay(){
                setTimeout(()=>{
                    console.log(this.name);
                })
            },
            layOut(){
                setTimeout(function(){
                    console.log(this.name);
                }.bind(this))
            },
            print(){
                var that = this;
                setTimeout(function(){
                    console.log(this.name);
                }.bind(that))
            }
        }
        obj.sayName();//javascript
        obj.wait();//window
        obj.delay();//javascript
        obj.layOut();//javascript
        obj.print();//javascript
    </script>

3-构造函数和class中

#this指向使用new关键字实例化的对象
function Fun(){
    console.log(this);  //this指向的是fun 实例对象  指向创造的新对象，新对象赋值给了fun
}
var fun = new Fun()
class Person{
            skill = "vue";
            constructor(name,age){
                this.name = name;
                this.age = age;
            }
        }
        var p = new Person("lisi",18);
        console.log(p.name); //lisi

4-call、bind、apply

this指向当前上下文的this
<script>
        function fn1(){
            console.log(this);
        }
        var obj = {
            name:"vue"
        }
        fn1.call(obj)
        fn1();
        var fn2 = fn1.bind(obj);
        fn2()
</script>