javascript

Chapter 8: The Browser Object Model
If the OK button is clicked, prompt() returns the value in the text box; if Cancel is clicked or the dialog
is otherwise closed without clicking OK, the function returns null . Here ’ s an example:
var result = prompt(“What is your name? “, “”);
if (result !== null) {
alert(“Welcome, “ + result);
}
These system dialogs can be helpful for displaying information to the user and asking for confirmation
of decisions. Since they require no HTML, CSS, or JavaScript to be loaded, they are fast and easy ways to
enhance a web application.
Google Chrome introduced a new feature regarding these system dialogs. If the actively running script
produces two or more system dialogs during its execution, each subsequent dialog after the first displays
a check box that allows the user to disable any further dialogs until the page reloads (see Figure 8 - 6 ).
Figure 8-6
When the check box is checked and the dialog box is dismissed, all further system dialogs (alerts,
confirms, and prompts) are blocked until the page is reloaded. Chrome 0.2 gives the developer no
indication as to whether the dialog was displayed. The dialog counter resets whenever the browser is
idle, so if two separate user actions produce an alert, the check box will not be displayed in either; if a
single user action produces two alerts in a row, the second will contain the check box. It ’ s expected that
this feature will be refined to give developers more information about the success of the dialogs by the
time the browser reaches version 1.0.
Two other types of dialogs can be displayed from JavaScript: find and print. Both of these dialogs are
displayed asynchronously, returning control to the script immediately. The dialogs are the same as the
ones the browser employs when the user selects either Find or Print from the browser ’ s menu. These are
displayed using the find() and print() methods on the window object as follows:
//display print dialog
window.print();
//display find dialog
window.find();
These two methods give no indication as to whether the user has done anything with the dialog, so it is
difficult to make good use of them. Further, since they are asynchronous, they don ’ t contribute to
Chrome ’ s dialog counter and won ’ t be affected by the user opting to disallow further dialogs.
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