XX笔试题，node和浏览器环境下的输出分别是什么，为什么会有不同？

    var num = 1;
    var myObject = {
      num: 2,
      add: function () {
        this.num = 3;
        (function () {
          console.log(this.num);
          this.num = 4;
        })()
        console.log(this.num);
      },
      sub: function () {
        console.log(this.num);
      }
    }
    myObject.add()
    console.log(myObject.num);
    console.log(num);
    var sub = myObject.sub;
    sub();