undefined 和 is not defined
//1
console.log(a); // is not defined
//2
var a;
console.log(a); //undefined
//3
console.log(a); //undefined
var a = 10;
//1
console.log(a); // is not defined
//2
var a;
console.log(a); //undefined
//3
console.log(a); //undefined
var a = 10;
转载于:https://www.cnblogs.com/hukuangjie/p/11186273.html