Function normalizeEmitsOptions

packages/runtime-core/src/componentEmits.ts:238–291

(
  comp: ConcreteComponent,
  appContext: AppContext,
  asMixin = false,
)

const mixinEmitsCache = new WeakMap<ConcreteComponent, ObjectEmitsOptions>()
export function normalizeEmitsOptions(
  comp: ConcreteComponent,
  appContext: AppContext,
  asMixin = false,
): ObjectEmitsOptions | null {
  const cache =
    __FEATURE_OPTIONS_API__ && asMixin ? mixinEmitsCache : appContext.emitsCache
  const cached = cache.get(comp)
  if (cached !== undefined) {
    return cached
  }

  const raw = comp.emits
  let normalized: ObjectEmitsOptions = {}

  // apply mixin/extends props
  let hasExtends = false
  if (__FEATURE_OPTIONS_API__ && !isFunction(comp)) {
    const extendEmits = (raw: ComponentOptions) => {
      const normalizedFromExtend = normalizeEmitsOptions(raw, appContext, true)
      if (normalizedFromExtend) {
        hasExtends = true
        extend(normalized, normalizedFromExtend)
      }
    }
    if (!asMixin && appContext.mixins.length) {
      appContext.mixins.forEach(extendEmits)
    }
    if (comp.extends) {
      extendEmits(comp.extends)
    }
    if (comp.mixins) {
      comp.mixins.forEach(extendEmits)
    }
  }

  if (!raw && !hasExtends) {
    if (isObject(comp)) {
      cache.set(comp, null)
    }
    return null
  }

  if (isArray(raw)) {
    raw.forEach(key => (normalized[key] = null))
  } else {
    extend(normalized, raw)
  }

  if (isObject(comp)) {
    cache.set(comp, normalized)
  }
  return normalized
}

// Check if an incoming prop key is a declared emit event listener.
// e.g. With `emits: { click: null }`, props named `onClick` and `onclick` are