0x000
vo(g)obj1 = 0x001obj2 = 0x000
vo（g）：全局执行变量obj1 = 0x000（存放的是地址)obj2
EC（G）全局执行上下文
x:100y:0x001
ECstack 执行环境栈
var obj1 = {x: 100}var obj2 = obj1obj2['x'] = 200console.log(obj1.x)
堆内存 heap {x: 100} 0x000
0x001
var obj1 = { x: 100 }var obj2 = obj1obj1.y = obj1 = { x: 200 }// 先执行obj1.y = {x:200}console.log(obj1.y)console.log(obj2)
x:200
x: 100 ---》 200
