Function has

packages/reactivity/src/collectionHandlers.ts:130–143

(this: CollectionTypes, key: unknown)

      return target.size
    },
    has(this: CollectionTypes, key: unknown): boolean {
      const target = this[ReactiveFlags.RAW]
      const rawTarget = toRaw(target)
      const rawKey = toRaw(key)
      if (!readonly) {
        if (hasChanged(key, rawKey)) {
          track(rawTarget, TrackOpTypes.HAS, key)
        }
        track(rawTarget, TrackOpTypes.HAS, rawKey)
      }
      return key === rawKey
        ? target.has(key)
        : target.has(key) || target.has(rawKey)
    },
    forEach(this: IterableCollections, callback: Function, thisArg?: unknown) {
      const observed = this
      const target = observed[ReactiveFlags.RAW]