JavaScript® 24-Hour Trainer

Chapter 26. Forms ― A Primer

In early versions of browsers, forms were generally the only means by which a web application could interact with the user. The user could input data into a variety of form controls and send that data to the server, and a server-side application would return a web page that incorporated the data in some way. In many cases a server-side application would have to validate every field in a form, and notify the user of any errors when responding to a form submission. This experience could be frustrating for the user, as sometimes one or more fields would be cleared of any data the user had entered.

Forms are still an important part of any web application that requires input from the user, but today's Web is far more sophisticated than that of yesteryear. With JavaScript, you can validate some form fields before any information is sent to the server — providing a much better experience for the user.

Over the course of the next few lessons, you learn how to script a variety of form controls. But first let's look at some basics of scripting forms with JavaScript.

FORMS AND THE DOM

A form in an HTML page is denoted by the <form/> element, and a single web page can have any number of forms. Quite naturally, the document object has a forms property — a collection of all <form/> elements found in the document. Like all array-like objects, document.forms has a length property, and you can access each form by specifying the index at which a form exists within the document, ...