Javascript [Electronic resources] : The Definitive Guide (4th Edition) نسخه متنی

Chapter 15. Forms and Form Elements

As we've seen in examples throughout this book, the use of HTML
forms is basic to almost all JavaScript programs. This chapter
explains the details of programming with forms in JavaScript. It is
assumed that you are already somewhat familiar with the creation of

HTML
forms and with the input elements that they contain. If not, you may
want to refer to a good book on HTML.[1] The client-side
reference section of this book lists the HTML syntax along with the
JavaScript syntax for forms and form elements; you may find these
useful for quick reference.

Submit
button (or unless it has only a single text input field and allows
the user to press the

Return key as
a shortcut for submission). With JavaScript, on the other hand, a

Submit button is never necessary
(unless the JavaScript program is working with a cooperating
server-side program, of course). With JavaScript, a form can have any
number of push buttons with event handlers that perform any number of
actions when clicked. In previous chapters, we've seen some of
the possible actions that such buttons can trigger: replacing one
image with another, using the location property to
load and display a new web page, opening a new browser window, and
dynamically generating a new HTML document in another window or
frame. As we'll see later in this chapter, a JavaScript event
handler can even trigger a form to be submitted.

As we've seen in examples throughout this book, event handlers
are almost always the central element of any interesting JavaScript
program. And the most commonly used event handlers (excluding the
event handlers of the Link object) are those used with forms or form
elements. This chapter introduces the JavaScript Form object and the
various JavaScript objects that represent form elements. It concludes
with an example that illustrates how you can use JavaScript to
validate user input on the client before submitting it to a
server-side program running on the web server.