Adds a waiter to a rective UI element. Thew waiter is displayed when the element is invalidated then is removed when the element receives a new value.
withWaiter(element, html = spin_1(), color = "#333e48", image = "")A reactive element, e.g.: uiOutput,
or plotOutput.
HTML content of waiter, generally a spinner, see spinners.
Background color of loading screen.
Path to background image.