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System dialogs

Aside from popping up new browser windows, several other methods

pop up

information to the user

utilizing methods of the

window

object:

alert()

confirm()

, and

input()

You are already familiar with the syntax of a call to

alert()

because it has been used in a large number

of examples up to this point. This method accepts one argument, which is the text to display to the user.

When

alert()

is called, the browser creates a system message box that displays the given text with an

OK button. For example, the following line of code causes the message box in Figure 5-6 to be displayed:

alert(“Hello world! “);

Figure 5-6

Alert dialogs are typically used when users must be made aware of something that they have no control

over, such as errors. Often alert dialogs are displayed when the user has entered invalid data into a form.

The second type of dialog is displayed 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 in the confirm dialog, which allows the user to indicate if a

given action should be taken. For example, the following line of code displays the confirm dialog shown

in Figure 5-7:

confirm(“Are you sure? “);

Figure 5-7

Opening new windows can be helpful to users in some instances, but generally

speaking it’s better to keep pop-up windows to a minimum. A large industry has

popped up (no pun intended) selling pop-up ads on Web sites, which most users

find incredibly annoying. To this end, many users have installed pop-up blockers

that automatically block all pop-up windows unless the user specifically allows

them. Remember, pop-up blockers don’t know the difference between a legitimate

pop-up window and an advertisement, so it’s always best to warn a user when a

window is going to be popped up.

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