var num = 10;fun();function fun() {` console.log(num);` var num = 20;`}>> undefined
因为在fun()
里,因为log()
调用了num
,就在这个函数的作用域里找 num
,然后把num
的声明提前,相当于是:
function fun() { var num; console.log(num); num = 20;}
另一个例子:
var a = 18;fun();function fun() { var b = 9; console.log(a); console.log(b); var a = 5;}>> undefined>> 9