gistfile1.js

var Modal = {
  controller: function() {
    return {isVisible: false} //internal state
  },
  view: function() {
    return m(".modal", {
      class: ctrl.visible ? ".modal-visible" : "" //sets visibility via CSS
      config: function(el, init) {
        if (!init) {
          //jQuery-exposed API
          $(el).data("modal", {
            toggle: function() {
              m.startComputation()
              ctrl.isVisible = !ctrl.isVisible
              m.endComputation()
            }
          })
        }
      }
    }, "modal!")
  }
}

//render the component via Mithril
m.mount(document.body, Modal)

//access it from outside
$(".modal:eq(0)").data("modal").toggle()