Extending existing shiny inputs

I am trying to extend the sliderInput() object with some specific javascript behavior. In R, I have made a new object SliderInputEnhanced that adds enhanced to the class attribute generated by sliderInput().

<input class="js-range-slider enhanced" ... />

Subsequently, I am writing Shiny binders as described here. I am mainly interested in using the onFinish callback of IonRangeSlider. This is my current code:

// step i
var binding = new Shiny.InputBinding();

// step ii
$.extend(binding, {

  find: function(scope) {
    // find all instances of class
    return $(scope).find(".js-range-slider.enhanced");
  },

  initialize: function(el){
    var irs = $(el);
    var data = irs.data();
    data.onFinish = function (data, scope) {
      // Some specific code...
    };

    irs.ionRangeSlider(data);
  }

});

// step iii
Shiny.inputBindings.register(binding);

This approach fails in the browser with "Uncaught Not implemented" from input_bindings.js on the following line: this.getValue = function(el) { throw "Not implemented"; };

Subsequently, I would have to implement the rest of the binder functions such as getValue(), but as I already stated, I merely want to extend the current js-range-slider with as little overhead as possible. What options do I have? Is my current approach sane?