javascript

Chapter 8: The Browser Object Model
Alert dialogs are typically used when users must be made aware of something that they have no control
over, such as an error. A user’s only choice is to dismiss the dialog after reading the message.
The second type of dialog is invoked by calling confirm() . A confirm dialog looks similar to an alert
dialog in that it displays a message to the user. The main difference between the two is the presence of a
Cancel button along with the OK button, which allows the user to indicate if a given action should be
taken. For example, confirm( “ Are you sure? ” ) displays the confirm dialog box shown in Figure 8 - 4 .
Figure 8-4
To determine if the user clicked OK or Cancel, the confirm() method returns a Boolean value: true if
OK was clicked, or false if Cancel was clicked or the dialog box was closed by clicking the X in the
corner. Typical usage of a confirm dialog looks like this:
if (confirm(“Are you sure?”)) {
alert(“I’m so glad you’re sure! “);
} else {
alert(“I’m sorry to hear you’re not sure. “);
}
In this example, the confirm dialog is displayed to the user in the first line, which is a condition of the if
statement. If the user clicks OK, an alert is displayed saying, “ I ’ m so glad you ’ re sure! ” If, however, the
Cancel button is clicked, an alert is displayed saying, “ I ’ m sorry to hear you ’ re not sure. ” This type of
pattern is often employed when the user tries to delete something, such as an e-mail message.
The final type of dialog is displayed by calling prompt() , which prompts the user for input. Along with
OK and Cancel buttons, this dialog has a text box where the user may enter some data. The prompt()
method accepts two arguments: the text to display to the user, and the default value for the text box
(which can be an empty string). Calling prompt( “ What ’ s your name? ” , “ Michael “ ) results in the
dialog box shown in Figure 8 - 5.
Figure 8-5
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