Not understanding XMLHTTP state: help?

[Dan Beanweed]

I am experimenting with XMLHTTP in a personal website. If I can understand it I would like to use it in a SVG application at work. But I don't get what's going on with my code, especially after reading the posts on this and other fora.

I create an object using "xmlhttp = new XMLHttpRequest();", no problem. Then I have this script:

 
function getContent(file){
    if(file==""){ return; }
    xmlhttp.onReadyStateChange=stateChange();
    xmlhttp.open("GET",file,true);  //async mode!
    xmlhttp.send(null);
}//end function getComments
 
function stateChange(){
    alert("state:"+xmlhttp.readyState);
    if (xmlhttp.readyState==4){  // the response is complete
     . . . 
     var itm = xmlhttp.responseXML;
     var text=itm.getElementsByTagName("content")[0].xml;
     document.getElementById('xmlcontent').innerHTML=text; 
     . . .
 
 

Then in the body of the page I have this list:

<form id="nulfrm" action="thispage.htm">
    <select name="past_comments" size="3" onchange="getContent(this.options[this.selectedIndex].value);">
        <option value="" selected>-- Select a topic from  below --</option>
        <option value="test1.xml" >Test</option>
        <option value="test2.xml">Other test</option>
    </select>
</form>
<div id="xmlcontent"></div>

Problem is when I run the page, it loads and no alert shows--as expected. Then I click on a list option and I get the alert message "state:0". When I close the alert nothing else happens. I can wait all day, no other messages appear. But if I then click on the other list item I get "state:4" and the message loads into the page like I wanted it to in the first place.

I think it must be an XMLHTTP issue since I am expecting more alerts than appear. But I am prepared to be wrong. Any help is appreciated.

[dmjpro]

I am experimenting with XMLHTTP in a personal website. If I can understand it I would like to use it in a SVG application at work. But I don't get what's going on with my code, especially after reading the posts on this and other fora.

I create an object using "xmlhttp = new XMLHttpRequest();", no problem. Then I have this script:

 
function getContent(file){
    if(file==""){ return; }
    xmlhttp.onReadyStateChange=stateChange();
    xmlhttp.open("GET",file,true);  //async mode!
    xmlhttp.send(null);
}//end function getComments
 
function stateChange(){
    alert("state:"+xmlhttp.readyState);
    if (xmlhttp.readyState==4){  // the response is complete
     . . . 
     var itm = xmlhttp.responseXML;
     var text=itm.getElementsByTagName("content")[0].xml;
     document.getElementById('xmlcontent').innerHTML=text; 
     . . .
 
 

Then in the body of the page I have this list:

<form id="nulfrm" action="thispage.htm">
    <select name="past_comments" size="3" onchange="getContent(this.options[this.selectedIndex].value);">
        <option value="" selected>-- Select a topic from  below --</option>
        <option value="test1.xml" >Test</option>
        <option value="test2.xml">Other test</option>
    </select>
</form>
<div id="xmlcontent"></div>

Problem is when I run the page, it loads and no alert shows--as expected. Then I click on a list option and I get the alert message "state:0". When I close the alert nothing else happens. I can wait all day, no other messages appear. But if I then click on the other list item I get "state:4" and the message loads into the page like I wanted it to in the first place.

I think it must be an XMLHTTP issue since I am expecting more alerts than appear. But I am prepared to be wrong. Any help is appreciated.

Welcome to TSDN
This is the error in this line.

xmlhttp.onReadyStateChange=stateChange();   //This is wrong.
xmlhttp.onReadyStateChange=stateChange;    //This one is right.
 

Best of luck with your try.
Kind regards,
Dmjpro.

[Dan Beanweed]

Welcome to TSDN
This is the error in this line.

xmlhttp.onReadyStateChange=stateChange();   //This is wrong.
xmlhttp.onReadyStateChange=stateChange;    //This one is right.
 

Best of luck with your try.
Kind regards,
Dmjpro.

Very kind of you to reply. However, if I make the change you suggest, then nothing at all happens: no alerts, no text, nothing.

Any other suggestions?

[acoder]

Very kind of you to reply. However, if I make the change you suggest, then nothing at all happens: no alerts, no text, nothing.

Any other suggestions?

Javascript is case-sensitive. Get rid of the caps:

xmlhttp.onreadystatechange=...

[Dan Beanweed]

Javascript is case-sensitive. Get rid of the caps:

xmlhttp.onreadystatechange=...

Brilliant 'acoder' and thanks. Case has never been a problem for me before, but your suggestion works perfectly.

[dmjpro]

Very kind of you to reply. However, if I make the change you suggest, then nothing at all happens: no alerts, no text, nothing.

Any other suggestions?

Hello Acoder really your eye is so perfect.
Really it's impressive.
I never gave attention to that line.

Anyway, Really you are very impressive.

Kind regards,
Dmjpro.

[acoder]

Brilliant 'acoder' and thanks. Case has never been a problem for me before, but your suggestion works perfectly.

No problem, you're welcome. Glad you got it working.

The reason for the strange behaviour earlier was that you were setting the result of calling the function to onReadyStateChange rather than the function itself. That's why you saw the alerts only once.

[pbmods]

Heya, Dan.

Have a look at this article.