Why does Bootstrap 4 use private methods in es6 classes?

Question

I was looking inside the source code of Bootstrap 4, and I discovered they're using es6 classes coupled with some revealing module pattern of some sort.

Here is a simplified example of code taken from here.

const Modal = (($) => {


  const NAME                         = 'modal'
  const VERSION                      = '4.0.0-alpha.3'
  ...

  const Default = {
    ...
  }


  class Modal {

    constructor(element, config) {
      this._config              = this._getConfig(config)
      this._element             = element
      ...
    }


    // public

    toggle(relatedTarget) {
      ...
    }

    show(relatedTarget) {
      ...
    }

    hide(event) {
      ...
    }

    dispose() {
      ...
    }


    // private

    _getConfig(config) {
      ...
    }

    _showElement(relatedTarget) {
      ...
    }

    _enforceFocus() {
      ...
    }

    _setEscapeEvent() {
      ...
    }

    _setResizeEvent() {
      ...
    }

  }

  return Modal

})(jQuery)

export default Modal

This would result in every method or property being exposed, including the private ones. However, this does not happen in the final product. For example, something like $('#myModal').modal('_getConfig') would not work. What is happening?

Answer 1

It's only adding one function to the jQuery prototype _jQueryInterface:

  $.fn[NAME]             = Modal._jQueryInterface
  $.fn[NAME].Constructor = Modal
  $.fn[NAME].noConflict  = function () {
    $.fn[NAME] = JQUERY_NO_CONFLICT
    return Modal._jQueryInterface
  }

  return Modal

})(jQuery)

If you look at the code of _jQueryInterface you'll see:

static _jQueryInterface(config, relatedTarget) {
  return this.each(function () {
    let data    = $(this).data(DATA_KEY)
    let _config = $.extend(
      {},
      Modal.Default,
      $(this).data(),
      typeof config === 'object' && config
    )

    if (!data) {
      data = new Modal(this, _config)
      $(this).data(DATA_KEY, data)
    }

    if (typeof config === 'string') {
      if (data[config] === undefined) {
        throw new Error(`No method named "${config}"`)
      }
      data[config](relatedTarget)
    } else if (_config.show) {
      data.show(relatedTarget)
    }
  })
}

If we look closely, you'll see that the instance of the class Modal is being saved as data:

    if (!data) {
      data = new Modal(this, _config)
      $(this).data(DATA_KEY, data)
    }

You can access it in the same fashion the script does it (but only after creating it for the first time):

let data    = $(this).data(DATA_KEY)

DATA_KEY is bs.modal

Edit:

$('#myModal').modal('_getConfig');

The function _getConfig is actually being called, it's just that function is returning the jQuery object not whatever the result of _getConfig is.