bootstrap-italia/src/js/plugins/track-focus.js

const DATA_MOUSE_FOCUS = 'data-focus-mouse'
const CLASS_NAME_MOUSE_FOCUS = 'focus--mouse'

class TrackFocus {
  constructor() {
    this._usingMouse = false

    this._bindEvents()
  }

  // Public

  // Private
  _bindEvents() {
    const events = ['keydown', 'mousedown']
    events.forEach((evtName) => {
      document.addEventListener(evtName, (evt) => {
        this._usingMouse = evt.type === 'mousedown'
      })
    })
    document.addEventListener('focusin', (evt) => {
      if (this._usingMouse) {
        if (evt.target) {
          evt.target.classList.add(CLASS_NAME_MOUSE_FOCUS)
          evt.target.setAttribute(DATA_MOUSE_FOCUS, true)
        }
      }
    })
    document.addEventListener('focusout', (evt) => {
      if (evt.target) {
        evt.target.classList.remove(CLASS_NAME_MOUSE_FOCUS)
        evt.target.setAttribute(DATA_MOUSE_FOCUS, false)
      }
    })
  }
}

/**
 * ------------------------------------------------------------------------
 * Data Api implementation
 * ------------------------------------------------------------------------
 */

new TrackFocus()

export default TrackFocus