预解析执行先后顺序

预解析执行先后顺序

情况一：
function fn1 () {
            var a, b, c = 9;
            console.log(a); //undefined
            console.log(b); //undefined
            console.log(c); //9
        }
        fn1();
        console.log("c=" + c); //报错，c is not defined 下面的二行不执行
        console.log("b=" + b);
        console.log("a=" + a);

        情况二：
        function fn2() {
            var a = b = c = 9;
            console.log(a); //9
            console.log(b); //9
            console.log(c); //9
        }
        fn2();
        console.log("c=" + c); //9
        console.log("b=" + b); //9
        console.log("a=" + a); //报错，a is not defined 
      										//  a 是局部变量，全局下找不到