JS Basic AJAX Coding Sample Code

  This article mainly introduces JS Basic Ajax writing, the need for friends can refer to the following

The code is as follows: var xmlhttp = null;  function Myajax () { //1, create XMLHttpRequest object  //2, You need to write different code   if (Windows) in different ways for IE and other browsers to create this object. XMLHttpRequest) { //for ff,mozilar,opera,safari,ie7,ie8  xmlhttp = new XMLHttpRequest (); //fix some browsers bug& nbsp if (xmlhttp.overridemimetype) {  xmlhttp.overridemimetype ("Text/xml"); } } else if (window. ActiveXObject) { //IE6 below for browsers   var activexname = ["MSXML2. XMLHTTP "," Microsoft.XMLHTTP "," ""];  for (var i = 0; i < activexname.length; i++) {  Try { //Remove a control name creation, if the creation succeeds then stops, conversely throws the exception   XMLHTTP = new ActiveXObject (activexname[i));  break;& nbsp catch (e) {} } }   //need to confirm XMLHTTP creation was successful   if (!xmlhttp) {  alert ("XMLHttpRequest Create failed!") ;  return; } else {  alert (XMLHTTP); }   //Registration callback function. Note the registration callback function is not parenthesized and adds the value of the function back to onreadystatechange  Xmlhttp.onreadystatechange = callback; //Set Connection information  // The first parameter represents the HTTP request method, which supports all HTTP request methods, mainly makingThe URL address of the request is represented by a get and post //second parameter, and the parameter requested by the Get method also represents an asynchronous or synchronous interaction in the urlkh //third interface parameter, true for the asynchronous   Xmlhttp.open ("Get" , "servlet/checkusername?username=" + UserName, True); //Send data representations and server-side interaction  //sync, send this will be done after server-side data comes back   Xmlhttp.send (NULL);   //asynchronous mode, send this sentence completes the execution of  //post mode request code  //xmlhttp.open immediately ("POST", " Servlet/checkusername ", True"; //post method requires you to set HTTP request headers  //xmlhttp.setrequestheader ("Content-type", " Application/x-www-form-urlencoded "); //post mode send data  //xmlhttp.send (" username= "+username); }   //Callback functions   function callback () { //Judge the state of the object is interactive completion   if (xmlhttp.readystate = 4) { //To determine whether HTTP interaction is successful   if (xmlhttp.status =) { //Get server-side returned data  //Get server-side output of plain text data   var responsetext = Xmlhttp.responset ext;  alert (responsetext); } } }