1 function getElementsByClassName(classStr,tagName,element){ 2     tagName = (tagName || ‘*‘); 3     element = (element || document); 4      5     if(typeof tagName == ‘object‘){ 6         element = tagName; tagName = ‘*‘; 7     } 8      9     if(document.getElementsByClassName){10         return element.getElementsByClassName(classStr);11     }else{12         var nodes = element.getElementsByTagName(tagName),13             ret = [];14         for(i = 0; i < nodes.length; i++) {15             if(hasClass(nodes[i],classStr)) ret.push(nodes[i]);16         }17         return ret;18     }19 20     function hasClass(tagStr,classStr){21         var arr=tagStr.className.split(/\s+/ ); //这个正则表达式是因为class可以有多个,判断是否包含22         for (var i=0;i<arr.length;i++){23             if (arr[i]==classStr) return true;24         }25         return false;26     };27 };