解决 IE 或者兼容模式不支持 document.getElementsByClassName() 的方法

网页错误详细信息
消息: 对象不支持此属性或方法

document.getElementsByClassName('element_name')

需要自己实现下该方法，因为ie5之前的版本并不支持这个方法

有以下四种方法，第四种兼容性最好

一、

//create method getElementsByClassName for document
    if(!document.getElementsByClassName){
        document.getElementsByClassName = function(className, element){
            var children = (element || document).getElementsByTagName('*');
            var elements = new Array();
            for (var i=0; i<children.length; i++){
                var child = children[i];
                var classNames = child.className.split(' ');
                for (var j=0; j<classNames.length; j++){
                    if (classNames[j] == className){
                        elements.push(child);
                        break;
                    }
                }
            }
            return elements;
        };
    }

二、

function getElementsByClassName(oElm, strTagName, strClassName){
    var arrElements = (strTagName == "*" && oElm.all)? oElm.all :
        oElm.getElementsByTagName(strTagName);
    var arrReturnElements = new Array();
    strClassName = strClassName.replace(/\-/g, "\\-");
    var oRegExp = new RegExp("(^|\\s)" + strClassName + "(\\s|$)");
    var oElement;
    for(var i=0; i < arrElements.length; i++){
        oElement = arrElements[i];
        if(oRegExp.test(oElement.className)){
            arrReturnElements.push(oElement);
        }
    }
    return (arrReturnElements)
}

三、

var getElementsByClass = function(searchClass,node,tag) {
        var classElements = new Array();
        if ( node == null )
                node = document;
        if ( tag == null )
                tag = '*';
        var els = node.getElementsByTagName(tag);
        var elsLen = els.length;
        var pattern = new RegExp("(^|\\s)"+searchClass+"(\\s|$)");
        for (i = 0, j = 0; i < elsLen; i++) {
                if ( pattern.test(els[i].className) ) {
                        classElements[j] = els[i];
                        j++;
                }
        }
        return classElements;
}

四、

var getElementsByClassName = function (searchClass, node,tag) {
  if(document.getElementsByClassName){
    var nodes =  (node || document).getElementsByClassName(searchClass),result = [];
      for(var i=0 ;node = nodes[i++];){
        if(tag !== "*" && node.tagName === tag.toUpperCase()){
          result.push(node)
        }
      }
      return result
    }else{
      node = node || document;
      tag = tag || "*";
      var classes = searchClass.split(" "),
      elements = (tag === "*" && node.all)? node.all : node.getElementsByTagName(tag),
      patterns = [],
      current,
      match;
      var i = classes.length;
      while(--i >= 0){
        patterns.push(new RegExp("(^|\\s)" + classes[i] + "(\\s|$)"));
      }
      var j = elements.length;
      while(--j >= 0){
        current = elements[j];
        match = false;
        for(var k=0, kl=patterns.length; k<kl; k++){
          match = patterns[k].test(current.className);
          if (!match)  break;
        }
        if (match)  result.push(current);
      }
      return result;
    }
  }

原文地址：http://blog.csdn.net/u011483807/article/details/49177147