Function forEach

packages/reactivity/src/collectionHandlers.ts:144–156

(this: IterableCollections, callback: Function, thisArg?: unknown)

        : target.has(key) || target.has(rawKey)
    },
    forEach(this: IterableCollections, callback: Function, thisArg?: unknown) {
      const observed = this
      const target = observed[ReactiveFlags.RAW]
      const rawTarget = toRaw(target)
      const wrap = shallow ? toShallow : readonly ? toReadonly : toReactive
      !readonly && track(rawTarget, TrackOpTypes.ITERATE, ITERATE_KEY)
      return target.forEach((value: unknown, key: unknown) => {
        // important: make sure the callback is
        // 1. invoked with the reactive map as `this` and 3rd arg
        // 2. the value received should be a corresponding reactive/readonly.
        return callback.call(thisArg, wrap(value), wrap(key), observed)
      })
    },
  }

  extend(