{

    let x = {color:"blue"};

    let y = x;

    let z = 3;

    {

        //重复定义x，所以对全局变量x进行了变量屏蔽

        let x = 5;

        console.log(x);

        //未重定义y，所以变量y.color不变

        console.log(y.color);

        //x已经被重定义，所以x.color不存在，undefined

        console.log(x.color);

        //直接是对对象y的修改，

        //let y = {color:"red"} 前面对y的引用会报错undefined

        y.color = "red";

        console.log(z);

    }

    console.log(x.color);//red

    console.log(y.color);//red

    console.log(z)//

}