Variable scope from XMLHttpRequest Callback

Dear All

I am trying to implement and XMLHttpRequest call for form validation.

I have the code working where it checks to see if an email address supplied already exists. This works, and so does the form validation, however the problem lies within a variable scope issue. The global variable errors is used to let the user know what errors there are with the form. I have declared the variable as a global variable and yet when I set it to nothing from within the XMLHttpRequest function call it treats it as a local variable. If I don't set it to nothing the function works apart from an ever increasing error string.

Not really sure where I am going wrong so any comments are very welcome.

Here is the code for the XMLHttpRequest and form validation function.

<script>
<!--
var request = false;
var smt = false;


// Initiate the XMLHTTP Request object

try {
	request = new XMLHttpRequest();
	//alert("XMLHttpRequest Created");
} catch (trymicrosoft) {
	try {
		request = new ActiveXObject("Msxml2.XMLHTTP");
		//alert("Msxml2.XMLHTTP created");
	} catch (othermicrosoft) {
		try {
			request = new ActiveXObject("Microsoft.XMLHTTP");
			//alert("Microsoft.XMLHTTP created");
			} catch(failed) {
				request = false;
			}
		}
	}
// alert if not initialised	
if (!request)
	alert("Error initialising XMLHttpRequest!");

// email checking function	
function getEmail() {

var e = document.form1.Email.value;
var url="checkemail.asp?q="+escape(e);
request.open("GET", url, true);
request.onreadystatechange = updatepage;
request.send(null);
}

function updatepage() {
//alert(request.readyState);
//alert(request.status);
if (request.readyState ==4)
	if (request.status ==200) {

		if (request.responseText!=0) {
		errors+="Email already exists\n";
		}
	
	} else {
	alert ("Error: "+ request.status);
	}
}	
	
	
function check() {
errors = ""; <---- This line seems to cause the scope problem *****
getEmail();

//alert(request.onreadystatechange);

//alert("Error report from check() function after email check call\n:"+errors);
var f = document.form1;
var em = f.Email.value.indexOf('@');

if (!f.Email.value) {
	errors+='Email rqd\n';
	} else {
	if (em==-1) {
	errors += 'Correct Email Address\n';
	}}
	

if (!f.Firstname.value) { errors+='Firstname rqd\n'; }
if (!f.Surname.value) {errors += 'Surname rqd\n';}
if (!f.Address1.value) {errors+='Address Line rqd\n';}
if (!f.City.value) {errors+='City rqd\n';}
if (!f.County.value) {errors+='County rqd\n';}
if (!f.Postcode.value) {errors+='Postcode rqd\n';}
if (!f.Country.value) {errors+='Country rqd\n';}

if (errors) {
alert(errors);
return false;
} else {
return true;
}
}

//-->
</script>

Code (markup):

The other point is that when the Email form field is changed or exited the function is called.

Many thanks
Graham

 

Where is the errors variable used outside of the check() function?

I don't see the error variable declared anywhere in the code example? It only seems to be set in the beginning of the check function, and then displayed in an alert box at the end of the check() function. Is this correct?

What exactly is the problem? Is there no value in the error variable with the alert message is shown?