shiny/man/isolate.Rd

% Generated by roxygen2: do not edit by hand
% Please edit documentation in R/reactives.R
\name{isolate}
\alias{isolate}
\title{Create a non-reactive scope for an expression}
\usage{
isolate(expr)
}
\arguments{
\item{expr}{An expression that can access reactive values or expressions.}
}
\description{
Executes the given expression in a scope where reactive values or expression
can be read, but they cannot cause the reactive scope of the caller to be
re-evaluated when they change.
}
\details{
Ordinarily, the simple act of reading a reactive value causes a relationship
to be established between the caller and the reactive value, where a change
to the reactive value will cause the caller to re-execute. (The same applies
for the act of getting a reactive expression's value.) The \code{isolate}
function lets you read a reactive value or expression without establishing this
relationship.

The expression given to \code{isolate()} is evaluated in the calling
environment. This means that if you assign a variable inside the
\code{isolate()}, its value will be visible outside of the \code{isolate()}.
If you want to avoid this, you can use \code{\link[base:eval]{base::local()}} inside the
\code{isolate()}.

This function can also be useful for calling reactive expression at the
console, which can be useful for debugging. To do so, simply wrap the
calls to the reactive expression with \code{isolate()}.
}
\examples{
\dontrun{
observe({
  input$saveButton  # Do take a dependency on input$saveButton

  # isolate a simple expression
  data <- get(isolate(input$dataset))  # No dependency on input$dataset
  writeToDatabase(data)
})

observe({
  input$saveButton  # Do take a dependency on input$saveButton

  # isolate a whole block
  data <- isolate({
    a <- input$valueA   # No dependency on input$valueA or input$valueB
    b <- input$valueB
    c(a=a, b=b)
  })
  writeToDatabase(data)
})

observe({
  x <- 1
  # x outside of isolate() is affected
  isolate(x <- 2)
  print(x) # 2

  y <- 1
  # Use local() to avoid affecting calling environment
  isolate(local(y <- 2))
  print(y) # 1
})

}

# Can also use isolate to call reactive expressions from the R console
values <- reactiveValues(A=1)
fun <- reactive({ as.character(values$A) })
isolate(fun())
# "1"

# isolate also works if the reactive expression accesses values from the
# input object, like input$x
}