Method reduce

packages/core/src/storages/dataset.ts:586–607

(
        iteratee: DatasetReducer<T, Data>,
        memo?: T,
        options: DatasetIteratorOptions = {},
    )

    async reduce<T>(iteratee: DatasetReducer<T, Data>, memo: T, options?: DatasetIteratorOptions): Promise<T>;

    async reduce<T = Data>(
        iteratee: DatasetReducer<T, Data>,
        memo?: T,
        options: DatasetIteratorOptions = {},
    ): Promise<T | undefined> {
        checkStorageAccess();

        let currentMemo: T | undefined = memo;

        const wrappedFunc: DatasetConsumer<Data> = async (item, index) => {
            if (index === 0 && currentMemo === undefined) {
                currentMemo = item;
            } else {
                // We are guaranteed that currentMemo is instanciated, since we are either not on
                // the first iteration, or memo was already set by the user.
                currentMemo = await iteratee(currentMemo as T, item, index);
            }
        };

        await this.forEach(wrappedFunc, options);
        return currentMemo;
    }

    /**
     * Iterates over dataset items using an async generator,