初学AJAX，基础问题 - Web 开发 / Ajax
<!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><script language="javascript"> var currentPage = 1; var xmlhttp = null; function getXmlhttp() { return new ActiveXObject("microsoft.xmlhttp"); } function previous() { currentPage --; setTimeout("getData()","1000"); } function next() { currentPage ++; setTimeout("getData()","1000"); } function getData() { if (xmlhttp == null) { ////这里，如果我加上IF，程序只能正确调用这个getData方法一次，以后再调用这个方法就拿不到数据！如果把IF块去掉，就行了，这是为什么？ xmlhttp = getXmlhttp(); xmlhttp.onreadyStateChange = readystate; } xmlhttp.open("get","http://b9426f32195d423:8080/ajax/servlet/ajax?page="+currentPage+"&math="+Math.random(),true); xmlhttp.send(null); } function readystate() { if (xmlhttp != null) { if (xmlhttp.readystate == 4) { if (xmlhttp.status == 200) { var table = document.all["table"]; var tbody = table.tBodies[1]; var xml = xmlhttp.responseXml; var arr = xml.getElementsByTagName("note"); if (arr.length == 0) { alert("没有数据!"); return; } var length = tbody.rows.length; for (var ac = length;ac>0;ac--) { tbody.deleteRow(tbody.rows[ac]); } table.setAttribute("border","1"); for (var i = 0;i<arr.length;i++) { tbody.insertRow(i); var node = arr[i]; var chi = node.childNodes; for (var a = 0;a<chi.length;a++) { tbody.rows[i].insertCell(a); tbody.rows[i].cells[a].appendChild(document.createTextNode(chi[a].text)); } } document.body.removeChild(document.getElementById("dddd")); ////还有这里，为什么这个层删不掉呢？它一直显示在网页上！ alert("done"); } else { alert("读取数据出错!"); } } else if (xmlhttp.readystate == 1) { var div = document.createElement("div"); div.style.borderStyle = "solid"; div.style.borderColor = "#333333"; div.style.borderWidth = "2px"; div.style.backgroundColor = "blue"; div.style.fontWeight = "bold"; div.style.fontSize = "14px"; div.style.width = "200px"; div.style.height = "25px"; div.style.textAlign = "center"; div.style.color = "yellow"; div.innerHTML = "正在读取....."; div.style.position = "absolute"; div.style.left = (parseInt(document.body.clientWidth) - 200) + "px"; div.style.top = "0px"; div.setAttribute("id","dddd"); document.body.appendChild(div); } } }</script></head><body onload="getData()"><table id="table"><tbody><tr> <th>ID</th> <th>NAME</th> <th>CONTENT</th></tr></tbody><tbody></tbody></table><a href="javascript:previous();">上一页</a> <a href="javascript:next();">下一页</a></body></html>