连续赋值

js中连续赋值问题（关键理解下图，就可以明白）

https://segmentfault.com/a/1190000008475665

如有帮助，请感谢sf作者！！！

var a = {n: 1};
var b = a;  
a.x = a = {n: 2};

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