js 求前n项的 fibnaci 数列和

     function f(n) {
         var num1 = 1,
             num2 = 1;
         if (n == 1)
             document.write(num1);//n=1,输出1
         else if (n > 1) {
             document.write(num1 + " " + num2 + " ");//n>=2;先输出前2项
             for (var i = 3; i < n; i++) {
                 var result = num1 + num2;
                 document.write(result + " ");
                 num1 = num2;
                 num2 = result;
             }
         }

     }
     f(3);