AJAX: sending xmlhttp requests in a loop
I have this function below and I call that function in a loop I get the 开发者_C百科alert n times but only n-1 or sometimes n-2 responses
if (window.XMLHttpRequest)
{// code for IE7+, Firefox, Chrome, Opera, Safari
xmlhttp=new XMLHttpRequest();
}
else
{// code for IE6, IE5
xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
}
xmlhttp.onreadystatechange=function()
{
if (xmlhttp.readyState==4 && xmlhttp.status==200)
{
alert(xmlhttp.responseText);
//document.getElementById("warnings_panel").innerHTML+=xmlhttp.responseText;
}
}
alert("in ajax)
xmlhttp.open("GET","getresponse.php?start="+ start + "&end=" + end,true);
xmlhttp.send();
I have made a class (that you can modify easily) for calling a function in loop and it calls the functions correctly. Maybe this could apply to your need.
(Also if anyone sees something wrong it's good to hear from others)
test.htm
<html>
<head>
<script type="text/javascript">
function myXmlHttp() {
/*constructor simulator*/
this.setPersitent=
function (file, onReadyFunc,params,loop)
{
myXmlHttpObj.loop = loop;
myXmlHttpObj.file=file;
myXmlHttpObj.onReadyFunc='myXmlHttpObj.'+onReadyFunc;
myXmlHttpObj.params=params;
myXmlHttpObj.mySetRequest();
}
this.setParams=
function ( params )
{
myXmlHttpObj.params=params;
}
<!--Standard initial code-->
this.mySetRequest =
function ()
{
request = false;
try { request = new XMLHttpRequest(); }
catch (trymicrosoft) {
try { request = new ActiveXObject("Msxml2.XMLHTTP"); }
catch (othermicrosoft) {
try {request = new ActiveXObject("Microsoft.XMLHTTP");}
catch (failed) {request = false;}/*catch3*/}/*catch2*/}/*catch1*/
if (!request)
alert("Error initializing XMLHttpRequest!");
} /*func*/
this.mySendReq=
function()
{
var url = myXmlHttpObj.file;
request.open("POST", url, true);
//Some http headers must be set along with any POST request.
request.setRequestHeader
("Content-type", "application/x-www-form-urlencoded;charset=utf-8");
request.setRequestHeader("Content-length", myXmlHttpObj.params.length);
request.setRequestHeader("Connection", "close");
request.onreadystatechange = eval(myXmlHttpObj.onReadyFunc);
request.send(myXmlHttpObj.params);
}
this.listenPHP =
function ( ) {
if ( request.readyState == 4) {
if ( request.status == 200)
{
alert(request.responseText);
myXmlHttpObj.loop--;
if(myXmlHttpObj.loop>0)
{
myXmlHttpObj.setParams("js_rand="+Math.random()+"");
myXmlHttpObj.mySendReq();
}
}//inner if
else{alert("status is " + request.status);}
}//outer iff
}//function
}//END
myXmlHttpObj = new myXmlHttp();
myXmlHttpObj.setPersitent
('getresponse.php', 'listenPHP',"js_rand="+Math.random()+"",3) ;
myXmlHttpObj.mySendReq();
</script>
</head>
<body >
</body>
</html>
and getresponse.php
<?PHP
echo 'I recived this random from js:',$_POST['js_rand'],'
this rand is from php:',rand(1,9999);
?>
onreadystatechange gets terminated when your function ends because the xmlhttp object gets removed as it is not a global variable. Am I right?
Better would be to put only the AJAX request in a function, so that the xmlhttp object is only created once (I used a shorter version to create the xmlhttp object in this example).
var xmlhttp = window.XMLHttpRequest ? new XMLHttpRequest() : new ActiveXObject('Microsoft.XMLHTTP');
function request() {
xmlhttp.open('GET', 'getresponse.php?start=' + start + '&end=' + end, true);
xmlhttp.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
alert(xmlhttp.responseText);
}
}
xmlhttp.send(null);
}
Generally, this should work, but we need more information about how you actually run that loop to know what might be wrong.
I also added encodeURIComponent and changed the condition inside the callback function, because status isn't always 200 when readyState reaches 4.
function request(start, end) {
var xmlhttp;
if (window.XMLHttpRequest)
xmlhttp = new XMLHttpRequest();
else
xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
xmlhttp.open('GET', 'getresponse.php?start=' + encodeURIComponent(start) + '&end=' + encodeURIComponent(end), true);
xmlhttp.onreadystatechange = function () {
if (xmlhttp.readyState == 4)
if (xmlhttp.status == 200) {
alert(xmlhttp.responseText);
} else {
// status ≠ 200, output useful error message
}
};
xmlhttp.send();
}
加载中,请稍侯......
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