Javascript whats wrong here?

techguy

Hi,
currently learning AJAX from "Beginning javascript" (WROX).The code here is adirect copy from the book.

I keep getting the error "oHttp is undefined" in my browser.

Function to create xmlHttpRequest:

// Create and return an XmlHttpRequest object.
function createXmlHttpRequest()
{
	// XMLHttpRequest exists
	// i.e. Client is IE7+,FF,Opera,Safari etc..
	if(window.XMLHttpRequest)
	{
		var oHtttp = new XMLHttpRequest();
		document.write('Client is not IE5 or IE6');
		return oHttp;
	}
	// Else client is IE5 or IE6
	else if( window.ActiveXObject)
	{
		var versions = ["MSXML2.XmlHttp.6.0","MSXML2.XmlHttp.3.0"];
		
		// Try to create a XMLHttpRequest with the latest version.
		for(var i=0;i<versions.length; i++)
		{
			try
			{
				var oHttp = new activeXObject(versions[i]);
				document.write('Client is IE5 or IE6');
				return oHttp;
			}
			catch (error)
			{
				// Do nothing here
			}
		}
	}

	// If all of the above fails then the client is not AJAX compatible.
	return null;
}

From paeg body:

<script type="text/javascript">
	var oHttp = createXmlHttpRequest();
	
	oHttp.open("GET", "http://localhost/ajax/test.txt", false);
	oHttp.send(null);

	if(oHttp.status == 200)
	{
		alert('File found!');
	}
	else if(oHttp.status == 404)
	{
		alert('File not found!');
	}
	else
	{
		alert('An error occured while attempting to retrieve the file');
	}
</script>

What am I missing here..?

Thanks.

P.S. I feel silly now:(

Seth Brundle

Is the error in IE or FF or both?

techguy

Both,

In IE I get "oHttp is null or not an object".

dlofnep

Problem is your declaration has 3 t's.

"var oHtttp = new XMLHttpRequest();"

You need to either remove a T, or make reference to the oHtttp object.

techguy

Oops that seems to be a typo.

I have the spelling correct in my code. Also the new should be omitted. The line should be:

var oHttp = createXmlHttpRequest();

Seth Brundle

good spot dlofnep!

dlofnep

Yeah possibly, I'm not familiar with Ajax, just Java. I know when you are creating a new instance of an object, you need to use the new keyboard, maybe not here if you say so

In anycase, yeah - it was just the typo that was the issue. Anytime you see errors regarding an object being undefined - just check the declaration

dlofnep

kbannon wrote: »

good spot dlofnep!

Thanks

techguy

Oops, I think I was a little unclear about the error. For some reason the code in my script is fine but the code on here is wrong..

..So, I still have the problem. With or without the new keyword. With it I get a different error:

"oHttp.open is not a function"

dlofnep

Can you post the updated code?

techguy

dlofnep wrote: »

Can you post the updated code?

No problem.

library.js:

// Create and return an XmlHttpRequest object.
function createXmlHttpRequest()
{
	// XMLHttpRequest exists
	// i.e. Client is IE7+,FF,Opera,Safari etc..
	if(window.XMLHttpRequest)
	{
		var oHttp = new XMLHttpRequest();
		document.write('Client is not IE5 or IE6');
		return oHttp;
	}
	// Else client is IE5 or IE6
	else if( window.ActiveXObject)
	{
		var versions = ["MSXML2.XmlHttp.6.0","MSXML2.XmlHttp.3.0"];
		
		// Try to create a XMLHttpRequest with the latest version.
		for(var i=0;i<versions.length; i++)
		{
			try
			{
				var oHttp = new activeXObject(versions[i]);
				document.write('Client is IE5 or IE6');
				return oHttp;
			}
			catch (error)
			{
				// Do nothing here
			}
		}
	}

	// If all of the above fails then the client is not AJAX compatible.
	return null;
}

exerpt from html body:

<script type="text/javascript">
	var oHttp = createXmlHttpRequest();
	
	oHttp.open("GET", "http://www.google.com", false);
	try
	{
		oHttp.send(null);
	}
	catch  (error)
	{
		// do nothing.
	}
alert(oHttp.status);
	if(oHttp.status == 200)
	{
		alert('File found!');
	}
	else if(oHttp.status == 404)
	{
		alert('File not found!');
	}
	else
	{
		alert('An error occured while attempting to retrieve the file');
	}
</script>

Once the error with the three t's was fixed I got an uncaught exception error. I needed to put the oHttp.send(null) line in a try catch block.
The runs through fine now displaying the status etc.

Thanks for the help guys..

dlofnep

Congrats