js笔试题

1. 那个是正确的

   1.for (let index = 0; index < 12; index++) {};console.log(index);//错误
   2.const a = 12;a = 13;console.log(a);//错误
   3.const G = {a:3};console.log(G.a);G.b=12;console.log(G.b);// 3,12
   4.let [head,...tail] = [1,2,3,4];console.log(tail)// [2,3,4]

2. 请问输出的是 // GoodByeJack

   var name = 'world';
   (function () {
    var name;
    if (typeof name === "undefined") {
        name = 'Jack';
        console.log('GoodBye'+name)
    } else {
        console.log('hello'+name)
    }
   })();