I was wondering how people are handing their XMLHttpRequest objects. Reusing the object for successive calls or creating a new one? I am currently using both ways. I have an "update" polling system that is using the same XMLHttpRequest for the entire session. Then my app also has user generated commands where it creates a new xhr each time.
So far they both seem to be working fine. I was wondering if anyone has experience that points towards favoring one way over another.
I reuse them, but very, very, very carefully, and am not shy in creating a new one if the other one is in use. Reusing does seem to be very buggy at times.
I use this little function I wrote, I guess it's creating a new one each time. The only thing I don't like about it is the eval for the call back function, but I can't think of another way to reliably pass values from the initiation of the request to the call back function.
Code:
var x=4;
getReqObjPost("someurl.asp","param1=1¶m2=2","callBack(xml,"+x+")");
Code:
//*******************************************************
// Sends an asyncronous xmlhttp request using post
// Pass the URL, Querystring, and callback function (as a string)
//*******************************************************
function getReqObjPost(url,params,func)
{
if (window.XMLHttpRequest){
xmlhttp=new XMLHttpRequest();
}
else if (window.ActiveXObject){
if(new ActiveXObject("Microsoft.XMLHTTP")){
xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
}
else{
xmlhttp=new ActiveXObject("Msxml2.XMLHTTP");
}
}
xmlhttp.onreadystatechange=function(){
if(xmlhttp.readyState==4){
if(xmlhttp.status==200){
var str=xmlhttp.responseText;
var xml=xmlhttp.responseXML;
eval(func);
}
else{
noData(xmlhttp.status,url);
}
}
}
var now=new Date();
params=params + "&c_date"+now.getSeconds()+"=" + now;
xmlhttp.open("POST",url,true);
xmlhttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded; charset=UTF-8");
xmlhttp.send(params);
}
__________________
Helping to build a bigger box. - Adam Matthews
I use this little function I wrote, I guess it's creating a new one each time. The only thing I don't like about it is the eval for the call back function, but I can't think of another way to reliably pass values from the initiation of the request to the call back function.
Code:
var x=4;
getReqObjPost("someurl.asp","param1=1¶m2=2","callBack(xml,"+x+")");
Code:
var x=4;
getReqObjPost("someurl.asp","param1=1¶m2=2",function() { callBack(xml,x) });
Works fine. The anonymous function creates a closure over all the variables available in the current scope (e.g. x), which then is referenced as an argument to callBack.
var x=4;
getReqObjPost("someurl.asp","param1=1¶m2=2",function() { callBack(xml,x) });
Works fine. The anonymous function creates a closure over all the variables available in the current scope (e.g. x), which then is referenced as an argument to callBack.
Okay, I'm trying, but I guess I don't see how to execute the function when it is passed in that fashion. And in your example, if based on my code, the variable xml does not yet exist at the time you are initially passing it.
???
Code:
function getReqObjPost(url,params,func)
{
if (window.XMLHttpRequest)
{
xmlhttp=new XMLHttpRequest();
}
else if (window.ActiveXObject)
{
if(new ActiveXObject("Microsoft.XMLHTTP"))
{
xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
}
else
{
xmlhttp=new ActiveXObject("Msxml2.XMLHTTP");
}
}
xmlhttp.onreadystatechange=function()
{
if(xmlhttp.readyState==4)
{
if(xmlhttp.status==200)
{
var str=xmlhttp.responseText;
var xml=xmlhttp.responseXML;
callback=func; Doesn't work
func This either
}
else
{
noData(xmlhttp.status,url);
}
}
}
var now=new Date();
params=params + "&c_date"+now.getSeconds()+"=" + now;
xmlhttp.open("POST",url,true);
xmlhttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded; charset=UTF-8");
xmlhttp.send(params);
}
I'm calling it like this:
Code:
<script type="text/javascript">
window.onload=function(){
var x=4
getReqObjPost("test.asp","",function(){doIt(xml,x)});
}
function doIt(xml,m){
alert(m);
var content=toXHTML(xml.documentElement);
document.getElementById('container').appendChild(content);
}
</script>
__________________
Helping to build a bigger box. - Adam Matthews
There is another group of fun errors with status codes in th 12XXX. (IE errors)
I actually have code in my handlers that see this error and issue a retry attempt.
Good thing to do is look at Dojo, Prototype, and YUI on what they do under the covers. You will see notes on errors and other strange things. I have seen almost all of them in my logs at work. I log all clientside errors with a custom framework. Drives me insane with Object Expected and the boss expects you to know what the issue is with a line number!
Eric
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Tech Author [Ajax In Action, JavaScript: Visual Blueprint]
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