一个ajax类

lauphai

var xmlHttp;var state;function createXMLHttpRequest() {if(window.ActiveXObject) {xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");} else if(window.XMLHttpRequest) {xmlHttp = new XMLHttpRequest();}return xmlHttp;}function $(id){return document.getElementById(id);}function addOption(id,_json){var _s = $(id);_s.options.length = 1;for(var i=0;i<_json.length; i++){var option=new Option(_json[i].name,_json[i].value);_s.add(option);}}function getSelectOption(url,value,id){//alert("url--->"+url);//alert("value--->"+value);//alert("id--->"+id);state = id;getValue(url,value);}function getValue(url,value){xmlHttp = createXMLHttpRequest();xmlHttp.open("post",url,true);xmlHttp.setRequestHeader('Content-Type','application/x-www-form-urlencoded;charset=GBK');xmlHttp.onreadystatechange = handleStateChange;xmlHttp.send("value="+value);}function handleStateChange(){if(xmlHttp.readystate==4){if(xmlHttp.status==200){callBack();}}}function callBack(){var text = xmlHttp.responseText;var _json = eval(xmlHttp.responseText);addOption(state,_json);}通道   <select name="destnumber" id="destnunmberid" value="<%=destnumber!=null?destnumber:""%>" onchange="getSelectOption('http://localhost:8080/chan_all_json.jsp?routeid='+document.getElementById('operatorsid').value,this.value,'servicecode')">      <option value="">请选择通道</option>         <option value="82">82</option>         </select>业务代码<select id="servicecode" name="servicecode" value="<%=servicecode!=null?servicecode:""%>"><option value="" selected>请选择代码</option></select>