js里面的4种调用

1.方法调用

var obj = {
    name : "Nick",
    setSex : function () {
        console.log(this);//obj
        console.log(this.name);//Nick
    }
};

obj.setSex();

 2.apply 调用

var book = {
    
};

function getBookName(name){
    console.log(this);//book
    console.log(name);//hehe
}

getBookName.apply(book,["hehe"]);

3.构造函数调用

function Book(){
    this.title = "read";
    console.log(this);
    console.log(this.title);
}
Book.prototype.dosth = function() {
    // body...
    console.log(this);
    console.log(this.title);
};
Book.dosth2 = function(){
    console.log(this);
    console.log(this.title);
};
var book = new Book();
book.dosth();
Book.dosth2();
//Book内部以及原型链上的this指代了Book对象，而Book添加的函数dosth2里面this指代为Book这个函数

4.函数调用

function getThis (){
    console.log(this);//window
}
getThis();