mithril-updateEvent.js

function updateEvent(vnode, key, value) {
  if (vnode.events != null) {
    if (vnode.events[key] === value) return
    if (value != null && (typeof value === "function" || typeof value === "object")) {
      if (vnode.events[key] == null) vnode.dom.addEventListener(key.slice(2), vnode.events, false)
      vnode.events[key] = value
    } else {
      if (vnode.events[key] != null) vnode.dom.removeEventListener(key.slice(2), vnode.events, false) 
      vnode.events[key] = undefined
    }
  } else if (value != null && (typeof value === "function" || typeof value === "object")) {
    vnode.events = new EventDict()
    vnode.dom.addEventListener(key.slice(2), vnode.events, false)
    vnode.events[key] = value
  }
}