function isEmail (t)
      {
          s=t.value;
		  if (isEmpty(s))

           // is s whitespace?

           if (isWhitespace(s)) flg = false;
 
           // there must be >= 1 character before @, so we

           // start looking at character position 1

           // (i.e. second character)

           var i = 1;

           var sLength = s.length;

           // look for @

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

           { i++ ;

           }

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



           else flg = true;
           if (flg==false)
           {
             alert("You have not entered a valid email address!");
			 t.focus();
		   }
		  return flg;

		}

function isEmpty(s)

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

	}

function isWhitespace(s)
	{  var i;
 	  // Is s empty?

	  if (isEmpty(s)) return false;

 	   // Search through string's characters one by one

 	   // until we find a non-whitespace character.

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

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

 	  {   
 	       // Check that current character isn't whitespace.

 	       var c = s.charAt(i);

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

 	   // All characters are whitespace.

	    return true;

	}