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//the validation code comes from Hugh E. Williams and David Lane, "Web Database Application with PHP and MySQL"
//published by O'Reilly & Associates.
  
// A utility function that returns true if a string 
// contains only whitespace characters.
function isblank(s)
{
  for(var i = 0; i < s.length; i++)
  {
     var c = s.charAt(i);
     if ((c != ' ') &&
         (c != '\n') &&
         (c != '\t'))
        return false;
  }
  return true;
}

// This is the function that performs <form> validation.  
// It will be invoked from the onSubmit() event handler.
// The handler should return whatever value this function
// returns.
function verify(f)
{
  var msg;
  var empty_fields = "";
  var errors = "";

  // Loop through the elements of the form, looking for all
  // text and textarea elements that don't have an
  //  "optional" property defined.  Then, check for fields
  // that are empty and make a list of them.
  // Also, if any of these elements have a "min" or a "max"
  // property defined, then verify that they are numbers 
  // and that they are in the right range.
  // Put together error messages for fields that are wrong.
  for(var i = 0; i < f.length; i++)
  {
     var e = f.elements[i];

     if (((e.type == "text") ||
         (e.type == "textarea")) &&
         !e.optional)
     {
        // first check if the field is empty
        if ((e.value == null) ||
            (e.value == "") ||
            isblank(e.value))
        {
           empty_fields += "\n        " +
                           e.description;
           continue;
        }

        // Now check for fields that are supposed to be emails.
        if (e.email && !isblank(e.value))
        {
           var seenAt = false;
          
			var pattern = /^.+@.+\..{2,}$/;

			if (!(pattern.test(e.value)))
			{
				seenAt = false;
                append += "\n";
	        	if (append) {
              		errors += "- The field " + e.description + " must be valid";
				}
			}
			else
			{
    		   seenAt = true;
			}
        }

        // Now check for fields that are supposed 
        // not to have spaces
        if (e.nospaces)
        {
           var seenAt = false;
           var append = "";

           for(var j = 0; j < e.value.length; j++)
           {
              var c = e.value.charAt(j);

              if ((c == ' ') ||
                  (c == '\n') ||
                  (c == '\t'))
                 errors += "- The field " + e.description +
                           " must not contains white-space";
           }
        }

     } // if (type is text or textarea) and !optional
  } // for each character in field

  // Now, if there were any errors, then display the
  // messages, and return true to prevent the form from
  // being submitted.  Otherwise return false
  if (!empty_fields && !errors) 
     return true;

  msg  = "______________________________________________________\n\n"
  msg += "The form was not submitted because of the " +
         "following error(s).\n";
  msg += "Please correct these error(s) and re-submit.\n";
  msg += "______________________________________________________\n\n"

  if (empty_fields)
  {
     msg += "- The following required field(s) are empty:"
           + empty_fields + "\n";
     if (errors)
        msg += "\n";
  }
  msg += errors;
  alert(msg);
  return false;
}
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