Form Validation

Validation refers to the process of checking the contents of a user-submitted form before processing it. Most modern web forms contain some sort of validation to ensure that good data is passed through the form and all required fields are completed.

Client Side Validation

Client side validation means that the form's contents are checked by a script that runs on the user's computer (typically JavaScript). ColdFusion's <cfinput> tag allows you to easily and automatically generate client side validation.

Example:

Drawbacks to client side validation

The major problem with client side validation is that it relies on the user's computer to perform the validation. However, if a user has disabled JavaScript on their browser, they can bypass this client side validation. Therefore, it is a good idea to use client side validation in conjunction with server side validation, as explained below.

Server Side Validation

Server side validation means that the form data is passed to the web server, and a script is run to validate its contents on the web server. This is an important advantage over client side validation because the user can not disable it.

Example

A best practice: use them both!

It is considered best practice to use both client and server side validation. Although server side validation might be adequate by itself, relying on only server side validation means extra work for the web server, since every request MUST be sent to the server and processed. Since the majority of users have JavaScript enabled, client side validation will work just fine for them without having to use the web server for each form submission. By using both, you can make sure the form contains valid data and minimize the work the web server has to do.

Example: