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<table width="100%" summary="page for reactiveVal {shiny}"><tr><td>reactiveVal {shiny}</td><td style="text-align: right;">R Documentation</td></tr></table>

<h2>Create a (single) reactive value</h2>

<h3>Description</h3>

<p>The <code>reactiveVal</code> function is used to construct a &quot;reactive value&quot;
object. This is an object used for reading and writing a value, like a
variable, but with special capabilities for reactive programming. When you
read the value out of a reactiveVal object, the calling reactive expression
takes a dependency, and when you change the value, it notifies any reactives
that previously depended on that value.
</p>

<h3>Usage</h3>

<pre>
reactiveVal(value = NULL, label = NULL)
</pre>

<h3>Arguments</h3>

<table summary="R argblock">
<tr valign="top"><td><code>value</code></td>
<td>
<p>An optional initial value.</p>
</td></tr>
<tr valign="top"><td><code>label</code></td>
<td>
<p>An optional label, for debugging purposes (see
<code><a href="reactlog.html">reactlog()</a></code>). If missing, a label will be automatically
created.</p>
</td></tr>
</table>

<h3>Details</h3>

<p><code>reactiveVal</code> is very similar to <code><a href="reactiveValues.html">reactiveValues()</a></code>, except
that the former is for a single reactive value (like a variable), whereas the
latter lets you conveniently use multiple reactive values by name (like a
named list of variables). For a one-off reactive value, it's more natural to
use <code>reactiveVal</code>. See the Examples section for an illustration.
</p>

<h3>Value</h3>

<p>A function. Call the function with no arguments to (reactively) read
the value; call the function with a single argument to set the value.
</p>

<h3>Examples</h3>

<pre>

## Not run:

# Create the object by calling reactiveVal
r &lt;- reactiveVal()

# Set the value by calling with an argument
r(10)

# Read the value by calling without arguments
r()

## End(Not run)

## Only run examples in interactive R sessions
if (interactive()) {

ui &lt;- fluidPage(
  actionButton("minus", "-1"),
  actionButton("plus", "+1"),
  br(),
  textOutput("value")
)

# The comments below show the equivalent logic using reactiveValues()
server &lt;- function(input, output, session) {
  value &lt;- reactiveVal(0)       # rv &lt;- reactiveValues(value = 0)

observeEvent(input$minus, {
    newValue &lt;- value() - 1     # newValue &lt;- rv$value - 1
    value(newValue)             # rv$value &lt;- newValue
  })

observeEvent(input$plus, {
    newValue &lt;- value() + 1     # newValue &lt;- rv$value + 1
    value(newValue)             # rv$value &lt;- newValue
  })

output$value &lt;- renderText({
    value()                     # rv$value
  })
}

shinyApp(ui, server)

}

</pre>

<hr /><div style="text-align: center;">[Package <em>shiny</em> version 1.5.0 <a href="00Index.html">Index</a>]</div>
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