teal (version 1.1.0)

.call_once_when: Calls expression when condition is met

Description

Function postpones handlerExpr to the moment when eventExpr (condition) returns TRUE, otherwise nothing happens.

Usage

.call_once_when(
  eventExpr,
  handlerExpr,
  event.env = parent.frame(),
  handler.env = parent.frame(),
  ...
)

Value

An observer.

Arguments

eventExpr

A (quoted or unquoted) logical expression that represents the event; this can be a simple reactive value like input$click, a call to a reactive expression like dataset(), or even a complex expression inside curly braces.

handlerExpr

The expression to call whenever eventExpr is invalidated. This should be a side-effect-producing action (the return value will be ignored). It will be executed within an isolate() scope.

event.env

The parent environment for the reactive expression. By default, this is the calling environment, the same as when defining an ordinary non-reactive expression. If eventExpr is a quosure and event.quoted is TRUE, then event.env is ignored.

handler.env

The parent environment for the reactive expression. By default, this is the calling environment, the same as when defining an ordinary non-reactive expression. If handlerExpr is a quosure and handler.quoted is TRUE, then handler.env is ignored.

...

additional arguments passed to observeEvent with the exception of eventExpr that is not allowed.