Idocs Guide to HTML

Restricting a Field to Alphanumeric Only

JavaScript can be used to guide the user in entering correct data. This page describes a method for restricting entered data to just letters and numbers -- no spaces, commas or other types of characters are allowed. This technique is useful if you are asking for information such as a User ID which has only alphanumeric characters.

First, copy this JavaScript code into the <HEAD> section of your document:

<SCRIPT TYPE="text/javascript">
// copyright 1999 Idocs, Inc.
// Distribute this script freely but keep this notice in place
function letternumber(e)
var key;
var keychar;

if (window.event)
   key = window.event.keyCode;
else if (e)
   key = e.which;
   return true;
keychar = String.fromCharCode(key);
keychar = keychar.toLowerCase();

// control keys
if ((key==null) || (key==0) || (key==8) || 
    (key==9) || (key==13) || (key==27) )
   return true;

// alphas and numbers
else if ((("abcdefghijklmnopqrstuvwxyz0123456789").indexOf(keychar) > -1))
   return true;
   return false;

Using this script we can set a field as alphanumeric using the onKeyPress attribute. Use the exact onKeyPress attribute highlighted in this example. It is important that you use return in the attribute or the technique won't work..

User ID: <INPUT NAME=ID MAXLENGTH=8 onKeyPress="return letternumber(event)">

This creates this form:

User ID:

The next page shows a similar technique which allows you to restrict a field to just numbers.

Copyright 1997-2002 Idocs Inc. Content in this guide is offered freely to the public under the terms of the Open Content License and the Open Publication License. Contents may be redistributed or republished freely under these terms so long as credit to the original creator and contributors is maintained.