严格模式，函数禁止this指向window，下面函数中代码this 为 undefined
'use strict';
var a = function(){
console.log(this); //undefined
}
a()
for(var i = 0 ;i < 1;i++)
{
console.log(this); //window
}
f()
this 对象实在运行的时候基于函数的执行环境绑定的，当函数被作为某个对象的方法调用时，this等于那个对象。 匿名函数执行环境具有全局性，this通常指向window
var name = "The Window";
var object = {
name: "My Object",
getNameFunc: function() {
console.log(1,this.name);
},
getNameFunc2: function() {
return function(){
return function(){
console.log(2,this.name);
}
}
},
getNameFunc3: function(a) {
var foo = function(a){
console.log(3,this.name);
}
return foo;
}
};
var o2 = function(){
this.name = 'o2'; //this === window
object.getNameFunc();//My Object
object.getNameFunc3()(); // o2
}
o2()
object.getNameFunc(); //My Object
object.getNameFunc2()()(); // "The Window"
object.getNameFunc3()();//"The Window"
