Function patchEvent

packages/runtime-dom/src/modules/events.ts:36–68

(
  el: Element & { [veiKey]?: Record<string, Invoker | undefined> },
  rawName: string,
  prevValue: EventValue | null,
  nextValue: EventValue | unknown,
  instance: ComponentInternalInstance | null = null,
)

const veiKey: unique symbol = Symbol('_vei')

export function patchEvent(
  el: Element & { [veiKey]?: Record<string, Invoker | undefined> },
  rawName: string,
  prevValue: EventValue | null,
  nextValue: EventValue | unknown,
  instance: ComponentInternalInstance | null = null,
): void {
  // vei = vue event invokers
  const invokers = el[veiKey] || (el[veiKey] = {})
  const existingInvoker = invokers[rawName]
  if (nextValue && existingInvoker) {
    // patch
    existingInvoker.value = __DEV__
      ? sanitizeEventValue(nextValue, rawName)
      : (nextValue as EventValue)
  } else {
    const [name, options] = parseName(rawName)
    if (nextValue) {
      // add
      const invoker = (invokers[rawName] = createInvoker(
        __DEV__
          ? sanitizeEventValue(nextValue, rawName)
          : (nextValue as EventValue),
        instance,
      ))
      addEventListener(el, name, invoker, options)
    } else if (existingInvoker) {
      // remove
      removeEventListener(el, name, existingInvoker, options)
      invokers[rawName] = undefined
    }
  }
}

const optionsModifierRE = /(Once|Passive|Capture)$/
const optionsModifierEventRE = /^on:?(?:Once|Passive|Capture)$/