函数的执行环境和作用域
下面看一个例子：
var color = "blue";
function changeColor(){
var anotherColor = "red";
function swapColor(){
var tempColor = anotherColor;
console.log(tempColor);//red
anotherColor = color;
console.log(anotherColor);//blue
color = tempColor;
console.log(color);//red
}
swapColor();
}
changeColor();
