Event handler wrappers — event-wrappers • nacre

Control how event callbacks are dispatched from the browser to the server.

Usage

event_immediate(fn, coalesce = FALSE, prevent_default = FALSE)

event_throttle(
  fn,
  ms,
  leading = TRUE,
  coalesce = TRUE,
  prevent_default = FALSE
)

event_debounce(fn, ms, coalesce = TRUE, prevent_default = FALSE)

Arguments

fn: An event handler function receiving (event) or (event, id).
coalesce: If TRUE, gate on server idle so events never queue faster than the server can process them. Defaults to FALSE for event_immediate() and TRUE for event_throttle()/event_debounce().
prevent_default: If TRUE, call event.preventDefault() in the browser before dispatching. Defaults to FALSE.
ms: Minimum interval (throttle) or quiet period (debounce) in milliseconds.
leading: If TRUE (default), fire immediately on the first event. If FALSE, wait for the timer before firing.

Value

A wrapped handler.

Details

event_immediate(): Fires on every event with no rate limiting. Bare functions passed as event handlers are implicitly wrapped with event_immediate().
event_throttle(): Fires at most every ms milliseconds while the event is active.
event_debounce(): Waits until the user pauses for ms milliseconds before firing.

The event object

The event argument passed to handlers is a list containing all primitive-valued properties (string, numeric, logical) from the browser event object, plus these element properties:

value: The element's current value (character).
valueAsNumber: Numeric value of the element, or NA if the input is empty or non-numeric (e.g. a blank text box). Useful for range and number inputs.
checked: Logical, for checkbox and radio inputs.

Keyboard events additionally include key, code, ctrlKey, shiftKey, altKey, and metaKey.