JavaScript 2.0-The Complete Reference, Second ... - freecodingtutorial

window.confirm(string);
or simply
confirm(string);
where string is any valid string variable, literal, or expression that eventually evaluates to a
string value to be used as the confirmation question.
The confirm() method returns a Boolean value that indicates whether or not the information
was confirmed, true if the OK button was clicked and false if the window was closed or the
Cancel button was clicked. This value can be saved to a variable, like so
answer = confirm("Do you want to do this?");
or the method call itself can be used within any construct that uses a Boolean expression such
as an if statement, like the one here:
if (confirm("Do you want ketchup on that?"))
else
alert("Pour it on!");
alert("Hold the ketchup.");
Like the alert() method, confirmation dialogs should be browser modal.
The next example shows how the alert and confirm can be used.
JavaScript Power!