Web Database Applications with PHP and MySQL, 2nd Edition

JavaScript and Client-Side Validation

In this section, we introduce the JavaScript scripting language as a client-side method for validation and other simple tasks. JavaScript isn't a full-fledged programming language like PHP: it can't connect to databases, it offers only limited interaction with certain system resources, and it can't do most tasks a web database application requires. However, JavaScript is good for interacting with a form and for controlling the display of data to the user.

Client-side validation with JavaScript is optional but has benefits, including faster response to the user than server-side validation, a reduction in web server load, and a reduction in network traffic. Also, unlike server-side validation, it can be implemented as interactive validation where errors are checked as they occur and field-by-field reporting where error messages are shown individually. However, validation in the client tier is unreliable: the user can bypass the validation through design, error, or misconfiguration of their web browser. For that reason, client-side validation should be used only to improve speed, reduce load, and add features, and never to replace server-side validation.

Tip

The client-side scripting language we use here is best known as JavaScript. However, in June 1998, the European Computer Manufacturers Association (ECMA) agreed to be responsible for the standard implementations of the scripting language by Microsoft, Netscape, and Sun. Accordingly, the real ...