prompt method
window.prompt()
instructs the browser to display a dialog with an
optional message prompting the user to input some text, and to wait until
the user either submits the text or cancels the dialog.
Under some conditions — for example, when the user switches tabs — the browser may not actually display a dialog, or may not wait for the user to submit text or to cancel the dialog.
Implementation
external String? prompt([
String message,
String default_,
]);