mithril-event.js

// Here's an explanation of how this works:
// 1. The event names are always (by design) prefixed by `on`.
// 2. The EventListener interface accepts either a function or an object
//    with a `handleEvent` method.
// 3. The object does not inherit from `Object.prototype`, to avoid
//    any potential interference with that (e.g. setters).
// 4. The event name is remapped to the handler before calling it.
// 5. In function-based event handlers, `ev.target === this`. We replicate
//    that below.
// 6. In function-based event handlers, `return false` prevents the default
//    action and stops event propagation. We replicate that below.
function EventDict() {
  // Save this, so the current redraw is correctly tracked.
  this._ = currentRedraw
}
EventDict.prototype = Object.create(null)
EventDict.prototype.handleEvent = function (ev) {
  var handler = this["on" + ev.type]
  var result
  if (typeof handler === "function") result = handler.call(ev.currentTarget, ev)
  else if (typeof handler.handleEvent === "function") handler.handleEvent(ev)
  if (this._ && ev.redraw !== false) (0, this._)()
  if (result === false) {
    ev.preventDefault()
    ev.stopPropagation()
  }
}