JavaScript: The Definitive Guide, Fourth Edition

Name

Window.alert( ) — display a message in a dialog box

Availability

JavaScript 1.0

Synopsis

                  window.alert(message)

Arguments

message

The plain-text (not HTML) string to display in a dialog box popped up over window.

Description

The alert( ) method displays the specified message to the user in a dialog box. The dialog box contains an OK button that the user can click to dismiss the dialog box.

On Windows platforms, the dialog box displayed by alert( ) is modal, and JavaScript execution pauses until the user dismisses it. In Netscape 4 on Unix platforms, however, the alert( ) dialog box is nonmodal, and execution continues uninterrupted.

Usage

Perhaps the most common use of the alert( ) method is to display error messages when the user’s input to some form element is invalid in some way. The alert dialog box can inform the user of the problem and explain what needs to be corrected to avoid the problem in the future.

The appearance of the alert( ) dialog box is platform-dependent, but it generally contains graphics that indicate an error, warning, or alert message of some kind. While alert( ) can display any desired message, the alert graphics of the dialog box mean that this method is not appropriate for simple informational messages like “Welcome to my home page” or “You are the 177th visitor this week!”

Note that the message displayed in the dialog box is a string of plain text, not formatted HTML. You can use the newline character “\n” in your strings to break your message across ...