（十七）关于赋值引用变量

var obj = {n:1};
var obj2 = obj;
obj2.n = 2;
console.log(obj.n)	//2

var obj = {n:1};
function fn1(a){
	a.n = 3;	//将obj处的n的值改成了3
}
fn1(obj.n);	//2

var obj = {n:1};
function fn2(a){
	a = {n:4};	//只是改变了a；但是并没有改变obj的指向
}
fn2(obj.n);	//1

var a = {n:1};
var b = a;
a.x = a = {n:2};
console.log(a.n,b.n)	//2,1
console.log(a.x,b.x)	//undefined,{n:2}