Learning JavaScript

Chapter 7. Forms and JiT Validation

The JiT in this chapter’s title stands for Just-in-Time, an old manufacturing term that, in JavaScript lingo, represents timely forms validation that is triggered as the web-page reader makes her way through form fields. One of the most popular and useful JavaScript applications, JiT verifies form data before submitting it to the server, saving a round trip from page to server and back if the data is invalid or incomplete.

The hypertext link was the fuel, but forms were the matches that set the Web on fire. Web pages were, more or less, a curiosity—a way of putting information online—but the page interaction was one way: from the server to the reader. With the advent of forms and server-side processing, the whole concept of online shopping took off, and that’s all she wrote.

I remember when Amazon was a new site and a relatively new concept. It was a really ugly site, but it could take your order online and send what you wanted, and it didn’t need anything then except HTML and a little server-side processing. You still don’t need JavaScript to create or process forms; you only need it when you want to create and process forms well.

Accessing the Form

In JavaScript, forms are accessed through the DOM via the document object using a couple of different approaches. The first is to access the form using the forms property on document. Forms are just one of the many page elements collected in arrays. If the page only has one form, access ...