诠释JavaScript中的this

function UseThis(){
console.log(this === window);
this.instancePro = 1;
}
UseThis.objPro = 2;
UseThis.objMethod = function(){
console.log(this.objPro);
}
UseThis();//true 不管嵌套多深，执行函数时，函数内的this === window
console.log(instancePro);// 1

var useThis = new UseThis();//false 当前是A是个构造函数，构造函数内的this，是new创建的实例
console.log(useThis.instancePro);// 1

UseThis.objMethod();//2 当前函数是对象方法，this===UseThis
var fn = UseThis.objMethod;
fn();//undefined

/*函数两次调用call*/
function doubleBind() {
　　console.log(this.doubleVariable);
}
(function () {
　　console.log(this.doubleCalendar);//2
　　doubleBind.call({doubleVariable: 1});// 1
}).call({doubleVariable: 2});

/*由函数Bind绑定返回函数再调用call*/
function funBind() {
    console.log(this.pro);
}
var relFun = funBind.bind({pro: 2});
relFun.call({pro: 3});// 2

var con_inObj = {
   variable :"sprying",
   cons_fun:function(){
       console.log(this.variable);
   }
}
var new_obj = new con_inObj.cons_fun();//?

<!-- from 前端乱炖 -->
var x = 5;
var example = {
    x: 100,
    a: function () {
        var x = 200;
        console.log(‘a context: %s, var x = %s‘, this.x, x);
    },
    b: function () {
        var x = 300;
        return function () {
            var x = 400;
            console.log(‘b context: %s, var x = %s‘, this.x, x);
        };
    },
    c: function () {
        var other = {
            x: 500
        };
        var execB = this.b().bind(other);
        execB();
        return execB;
    }
}
console.log(‘example.x:‘ + example.x);
example.a();
example.b()();
example.a.call({
    x: 9999
});

var execB = example.c(); 
execB.call({
    x: 9999
});