Safe-wrapper of 'shiny' reactive function

A reactive expression whose errors never reach its consumers: an error is logged (and optionally shown) and the expression yields the last value it produced, or initial before its first success. Validation errors (req, validate) pass through, so outputs still stop rendering as they do with reactive.

Usage

safe_reactive(
  x,
  env = parent.frame(),
  quoted = FALSE,
  ...,
  label = NULL,
  domain = shiny::getDefaultReactiveDomain(),
  initial = NULL,
  error_wrapper = c("none", "notification", "alert")
)

Arguments

x, env, quoted, label, domain, ...

passed to reactive

initial

value returned while no evaluation has succeeded yet

error_wrapper

handler when error is encountered, choices are 'none' (log only), 'notification' (see error_notification), or 'alert' (see error_alert)

Value

'shiny' reactive expression

Details

'shiny' caches the error raised by a reactive expression and raises it again to every consumer until the expression is invalidated; when the consumer is an observer, or the expression is a trigger of bindEvent, the session is closed. The last good value therefore lives in this wrapper, not in the reactive's cache.

Examples

values <- shiny::reactiveValues(A = 1)

doubled <- safe_reactive({
  if (values$A < 0) { stop("A must be non-negative") }
  values$A * 2
})

# In a running app, `doubled()` keeps its last value when `values$A` turns
# negative; the error goes to the log instead of closing the session