给全局对象document添加一个getElementsByClassName方法.这样就可以通过类名来获得Dom对象了 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=gb2312" /> <title>无标题文档</title> <mce:script type="text/javascript"><!-- /** * 根据类名获得元素 * 参数说明: * 1、className 类名 * 2、tag 元素名 默认所有元素 * 3、elm 父元素 默认doucment */ document.getElementsByClassName = function(className, tag, elm) { var testClass = new RegExp("(^|/s)" + className + "(/s|$)"); var tag = tag || "*"; var elm = elm || document; var elements = (tag == "*" && elm.all)? elm.all : elm.getElementsByTagName(tag); var returnElements = []; var current; var length = elements.length; for(var i=0; i<length; i++){ current = elements[i]; if(testClass.test(current.className)){ returnElements.push(current); } } return returnElements; } window.onload = function(){ var divs = document.getElementsByClassName("div"); alert(divs.length); for(var i = 0; i < divs.length; i++){ alert(divs[i].id); } } // --></mce:script> </head> <body> <div class="div" id="div1"> </div> <div class="divvvv" id="div2"> <div class="div" id="div21"> </div> </div> <div class="div" id="div3"> </div> </body> </html>