js中没有getElementsByClassName怎么办

1 function getElementsByClassName (className) {
2   var all = document.all ? document.all : document.getElementsByTagName('*');
3   var elements = new Array();
4   for (var e = 0; e < all.length; e++) {
5     if (all[e].className == className) {
6        elements[elements.length] = all[e];
7       break;
8      }
9    }
10   return elements;
11 }
12