js 预解析案例

案例

f1();
    console.log(c);//9 没有var声明当全局变量看
    console.log(b);//9
    console.log(a);//报错
    function f1() {
        var a = b = c = 9;//等价于 var a=9;b=9;c=9;
        console.log(a);//9
        console.log(b);//9
        console.log(c);//9

    }