var whitespace = " \t\n\r";
var iEmail = "Please enter a valid email address (like your_name@company.com)"
var defaultEmptyOK = false
function isEmpty(s)
{   return ((s == null) || (s.length == 0))
}
function isWhitespace (s)
{   var i;
    if (isEmpty(s)) return true;
    for (i = 0; i < s.length; i++)
    {   
        var c = s.charAt(i);
        if (whitespace.indexOf(c) == -1) return false;
    }
    return true;
}
function warnInvalid (theField, s)
{   theField.focus()
    theField.select()
    alert(s)
    return false
}
function checkEmptyString (theField, s)
{  
 if (isWhitespace(theField.value)) 
       return warnInvalid (theField, s);
    else return true;
}
function isEmail (s)
{   if (isEmpty(s)) 
       if (isEmail.arguments.length == 1) return defaultEmptyOK;
       else return (isEmail.arguments[1] == true);
   
    // is s whitespace?
    if (isWhitespace(s)) return 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) != "@")) 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;
}

function checkEmail (theField, emptyOK)
{   if (checkEmail.arguments.length == 1) emptyOK = defaultEmptyOK;
    if ((emptyOK == true) && (isEmpty(theField.value))) return true;
    else if (!isEmail(theField.value, false)) 
       return warnInvalid (theField, iEmail);
    else return true;
}