var defaultEmptyOK = false

var whitespace = " \t\n\r";



// Check whether string s is empty.

function isEmpty(s)	{   

	return ((s == null) || (s.length == 0))

}

// Returns true if string s is empty or whitespace chars only.

function isWhitespace (s)	{   

	var i;



	if (isEmpty(s)) return true;



	// Search thru string's chars one by one

	// until we find a non-whitespace char.

	// When we do, return false; if we don't, return true.



	for (i = 0; i < s.length; i++)	{

		// Check that current char isn't whitespace.

		var c = s.charAt(i);

		if (whitespace.indexOf(c) == -1) return false;

	}



	// All chars are whitespace

	return true;

}



// isEmail (STRING s [, BOOLEAN emptyOK])

// 

// Email address must be of form 'a@b.c', i.e:

// * there must be at least one character before the @

// * there must be at least one character before and after the .

// * the characters @ and . are both required

//



function isEmail (s)	{



	if (isEmpty(s)) 

		if (isEmail.arguments.length == 1) return defaultEmptyOK;

		else return (isEmail.arguments[1] == true);



	if (isWhitespace(s)) return false;



	// there must be >= 1 character before @, so we

	// start looking at character position 1  (i.e. 2nd char)

	var i = 1;

	var sLength = s.length;



	// look for @

	while ((i < sLength) && (s.charAt(i) != "@"))	{ 

		i++

	}



	if ((i >= sLength) || (s.charAt(i) != "@")) return false;

	else i += 2;



	// look for .

	while ((i < sLength) && (s.charAt(i) != "."))	{

		i++

	}



	// there must be at least one character after the .

	if ((i >= sLength - 1) || (s.charAt(i) != ".")) return false;

	else return true;

}



// pass in the form's email field, e.g.

// onsubmit="return checkEmail(this.email_field);"

function checkEmail (f)	{

	var v = f.value;



	if (!isEmail(v))	{

		var errMsg = "Sorry, the email address you entered:\n";

		errMsg += v;

		errMsg += "\ndoes not appear to be valid.";



		alert (errMsg);



		f.select();

		f.focus();



		return false;  

	}

	else return true;



}