I'm using XMLHttpRequest
in JavaScript. However, it gives me an error, and I don't know what my problem is.
I have to parse an XML file and assign its contents to the webpage - here's my code:
<script = "text/javascript">
window.onload = onPageLoad();
var questionNum = 0;
function onPageLoad(questionNum) {
var xmlhttp = new XMLHttpRequest();
xmlhttp.open("GET","quiz.xml");
try {
xmlhttp.send(null); // Here a xmlhttprequestexception number 101 is thrown
} catch(err) {
document.getElementById("body").innerHTML += "\nXMLHttprequest error: " + err.description; // This prints "XMLHttprequest error: undefined" in the body.
}
xmlDoc = xmlhttp.responseXML;
parser = new DOMParser(); // This code is untested as it does not run this far.
}
</script>
My XML file is inside the same directory.
<question>
<query>what is 2+2?</query>
<option>4</option>
<option>5</option>
<option>3</option>
<answer>4</answer>
</question>
Just for reference, I typically program in C# or Java, and I'm running my website on Google Chrome.
This question is related to
javascript
ajax
xml
xmlhttprequest
I see 2 possible problems:
Problem 1
Solution: assign a callback function to the objects "onreadystatechange" -event and handle the data in that function
xmlhttp.onreadystatechange = callbackFunctionName;
Once the state has reached DONE (4), the response content is ready to be read.
Problem 2
Solution: Either use a try-catch for creating the correct object for correct browser ( ActiveXObject in IE) or use a framework, for example jQuery ajax-method
Note: if you decide to use jQuery ajax-method, you assign the callback-function with jqXHR.done()
The problem is likely to lie with the line:
window.onload = onPageLoad();
By including the brackets you are saying onload
should equal the return value of onPageLoad()
. For example:
/*Example function*/
function onPageLoad()
{
return "science";
}
/*Set on load*/
window.onload = onPageLoad()
If you print out the value of window.onload
to the console it will be:
science
The solution is remove the brackets:
window.onload = onPageLoad;
So, you're using onPageLoad
as a reference to the so-named function.
Finally, in order to get the response value you'll need a readystatechange
listener for your XMLHttpRequest
object, since it's asynchronous:
xmlDoc = xmlhttp.responseXML;
parser = new DOMParser(); // This code is untested as it doesn't run this far.
Here you add the listener:
xmlHttp.onreadystatechange = function() {
if(this.readyState == 4) {
// Do something
}
}
Source: Stackoverflow.com