ajax示例
//ajaxfunction retrieveURL(url,nameOfFormToPost) { //convert the url to a stringurl=url+getFormAsString(nameOfFormToPost); //Do the AJAX callif (window.XMLHttpRequest) { // Non-IE browsers req = new XMLHttpRequest(); req.onreadystatechange = processStateChange; try { req.open("GET", url, true); } catch (e) { alert("Server Communication Problem\n"+e); } req.send(null);} else if (window.ActiveXObject) { // IE req = new ActiveXObject("Microsoft.XMLHTTP"); if (req) { req.onreadystatechange=processStateChange; req.open("GET", url, true); req.send(); }}}//取到FOME中的参数function getFormAsString(formName){ //Setup the return StringreturnString =""; //Get the form valuesformElements=document.forms.elements; //loop through the array, building up the url//in the format '/strutsaction.do&name=value' for(var i=formElements.length-1;i>=0; --i ){ //we escape (encode) each value returnString+="&" +escape(formElements.name)+"=" +escape(formElements.value); } //return the values return returnString; }//这个是回调函数function processStateChange() {var info = document.getElementById("alert_message").value;if (req.readyState == 4) { // Complete if (req.status == 200) { // OK response //这里做回调的处理 var json = eval('(' + req.responseText + ')'); if(json.flag=='false'){ alert(json.message+""+info); }else if(json.flag=='true'){ doQuery(); }else if(json.flag=='somefalse'){ //清空删除列表 clearChecked(); alert(json.message+""+info); doQuery(); } /*//Split the text response into Span elements spanElements = splitTextIntoSpan(req.responseText); //Use these span elements to update the page replaceExistingWithNewHtml(spanElements); */ } else { alert("Problem with server response:\n " + req.statusText); }}}后台返回JSON数据如：{message:'xxx',flag:'xxx'}
ajax 拿到JSON使用var json = eval('(' + req.responseText + ')');
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