JavaScript & DHTML Cookbook, 2nd Edition

Chapter 8. Dynamic Forms

Introduction

Giving scripted intelligence to web forms was the impetus that led to the development of the JavaScript language and the notion of a document object model. While a lot has happened to scripting in the meantime, forms still make frequent use of scripts to assist with user-friendly instantaneous interaction that otherwise requires a two-way trip to the server (and delays for the user) to accomplish.

Because of the comparatively long history of scriptable forms and form controls, it is comforting to know that most such scripts work with a wide range of browsers, and not just those that implement the W3C DOM. Even so, there are some misunderstandings about the combination of scripts and forms that I’ll attempt to clear up in this chapter.

Referencing Forms and Controls

Before the W3C DOM, scripts used what is now known as DOM Level 0 syntax to reference form objects and the form controls (input and textarea elements) within them. This long-time convention relies for the most part on the form and controls having name attributes assigned to them. In fact, even today’s browsers won’t submit form control values to the server unless the elements have names assigned to them (independent of the now ubiquitous id attribute). At the same time, however, the object model provides arrays of forms and form elements, which can be accessed through JavaScript array syntax and numerical index values. For example, if a document contains a single form whose name is