JS——坑7

function f1(){         var tmp = 1;         this.x = 3;         console.log(tmp);         console.log(this.x);       }       var obj = new f1();  //1,3 实例化时会执行函数 坑       console.log(obj.x); //3       console.log(f1()); //1,3,undefined  函数没有返回值，则默认返回undefined