window.confirm() instructs the browser to display a dialog with an optional message, and to wait until the user either confirms 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 confirm or cancel the dialog.

message

A string you want to display in the confirmation dialog.

A boolean indicating whether OK (true) or Cancel (false) was selected. If a browser is ignoring in-page dialogs, then the returned value is always false.

if (window.confirm("Do you really want to leave?")) {
  window.open("exit.html", "Thanks for Visiting!");
}

Produces:

Dialog boxes are modal windows — they prevent the user from accessing the rest of the program's interface until the dialog box is closed. For this reason, you should not overuse any function that creates a dialog box (or modal window). Regardless, there are good reasons to avoid using dialog boxes for confirmation.

Alternatively <dialog> element can be used for confirmations.

• <dialog> element
• window.alert()
• window.prompt()