面试题:优先级问题

   let a = {x:1,y:2};
   let b = a;// 把对象a的空间地址赋值给变量b;
   a.y = a = {y:1};// 点的优先级最高；先运算a.y ;再运算a;
   console.log(a);// {y:1}
   console.log(b);//{x:1,y:{y:1}}