Register an Input Handler

Adds an input handler for data of this type. When called, Shiny will use the function provided to refine the data passed back from the client (after being deserialized by jsonlite) before making it available in the input variable of the server.R file.

registerInputHandler(type, fun, force = FALSE)

The type for which the handler should be added --- should be a single-element character vector.


The handler function. This is the function that will be used to parse the data delivered from the client before it is available in the input variable. The function will be called with the following three parameters:

  1. The value of this input as provided by the client, deserialized using jsonlite.

  2. The shinysession in which the input exists.

  3. The name of the input.


If TRUE, will overwrite any existing handler without warning. If FALSE, will throw an error if this class already has a handler defined.


This function will register the handler for the duration of the R process (unless Shiny is explicitly reloaded). For that reason, the type used should be very specific to this package to minimize the risk of colliding with another Shiny package which might use this data type name. We recommend the format of "packageName.widgetName".

Currently Shiny registers the following handlers: shiny.matrix, shiny.number, and

The type of a custom Shiny Input widget will be deduced using the getType() JavaScript function on the registered Shiny inputBinding.

See Also


  • registerInputHandler
# Register an input handler which rounds a input number to the nearest integer
registerInputHandler("mypackage.validint", function(x, shinysession, name) {
  if (is.null(x)) return(NA)

## On the Javascript side, the associated input binding must have a corresponding getType method:
getType: function(el) {
  return "mypackage.validint";

# }
Documentation reproduced from package shiny, version 1.5.0, License: GPL-3 | file LICENSE

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