Mengeluarkan tipe null dan undefined dari tipe data pada TypeScript

types.ts

export type Maybe<T> = T | null | undefined;
type UnpackArray<T> = T extends (infer U)[] ? U : T;
type Unpack<T, U> = U extends keyof T ? T[U] : never;

// type Post = { id: string; title: string; content: Maybe<string> };
type Post = {
  __typename?: 'Post';
  authorDatabaseId: Maybe<number>;
  authorId: Maybe<string>;
  bodyClasses: Maybe<string>;
  coAuthors: Maybe<string>;
  commentCount: Maybe<number>;
  commentStatus: Maybe<string>;
  content: Maybe<string>;
  databaseId: number;
  date: Maybe<string>;
  dateGmt: Maybe<string>;
  desiredSlug: Maybe<string>;
  enclosure: Maybe<string>;
  excerpt: Maybe<string>;
  featuredImageDatabaseId: Maybe<number>;
  featuredImageId: Maybe<string>;
  guid: Maybe<string>;
  id: string;
  isPreview: Maybe<boolean>;
  isRestricted: Maybe<boolean>;
  isRevision: Maybe<boolean>;
  isSticky: boolean;
  link: Maybe<string>;
  modified: Maybe<string>;
  modifiedGmt: Maybe<string>;
  pingStatus: Maybe<string>;
  pinged: Maybe<Array<Maybe<string>>>;
  previewRevisionDatabaseId: Maybe<number>;
  previewRevisionId: Maybe<string>;
  slug: Maybe<string>;
  status: Maybe<string>;
  title: Maybe<string>;
  toPing: Maybe<Array<Maybe<string>>>;
  uri: string;
};
type Posts = Maybe<Array<Maybe<Post>>>;
function getPostTitles(allPosts: Posts): Array<string> {
  return allPosts!.map((post) => post!.title!);
}

type PostDetailQueryType = { __typename?: 'RootQuery' } & {
  post: Maybe<
    { __typename?: 'Post' } & Pick<Post, 'id' | 'title' | 'content'> & {
        author: Maybe<
          { __typename?: 'NodeWithAuthorToUserConnectionEdge' } & {
            node: Maybe<
              { __typename?: 'User' } & Pick<User, 'slug' | 'name'> & {
                  avatar: Maybe<
                    { __typename?: 'Avatar' } & Pick<Avatar, 'url'>
                  >;
                }
            >;
          }
        >;
      }
  >;
};

type MaybeAuthor = NonNullable<PostDetailQueryType['post']>['author'];
type Author = NonNullable<NonNullable<PostDetailQueryType['post']>['author']>;
type PickMaybeAuthor = Unpack<
  NonNullable<PostDetailQueryType['post']>,
  'author'
>;
type PickAuthor = NonNullable<
  Unpack<NonNullable<PostDetailQueryType['post']>, 'author'>
>;

type Category = {
  __typename?: 'Category';
  count: Maybe<number>;
  databaseId: number;
  description: Maybe<string>;
  id: string;
  isRestricted: Maybe<boolean>;
  link: Maybe<string>;
  name: Maybe<string>;
  parentDatabaseId: Maybe<number>;
  parentId: Maybe<string>;
  slug: Maybe<string>;
  termGroupId: Maybe<number>;
  termTaxonomyId: Maybe<number>;
  uri: string;
};

type PostDetailWithCategoriesQuery = { __typename?: 'RootQuery' } & {
  post: Maybe<
    { __typename?: 'Post' } & Pick<Post, 'id' | 'title' | 'content'> & {
        categories: Maybe<
          { __typename?: 'PostToCategoryConnection' } & {
            nodes: Maybe<
              Array<
                Maybe<
                  { __typename?: 'Category' } & Pick<
                    Category,
                    'id' | 'slug' | 'name' | 'uri'
                  >
                >
              >
            >;
          }
        >;
      }
  >;
};

type CategoriesOnPost = NonNullable<
  Unpack<NonNullable<PostDetailWithCategoriesQuery['post']>, 'categories'>
>;
type CategoryNodes = Unpack<NonNullable<CategoriesOnPost>, 'nodes'>;
type PickMaybeCategory = UnpackArray<NonNullable<CategoryNodes>>;
type PickCategory = NonNullable<UnpackArray<NonNullable<CategoryNodes>>>;

Saya tidak tampilkan semua tipe disini seperti tipe User dan Avatar. Namun setidaknya tidak merusak tipe(ekstrak null dan undefined) yang jadi contoh utama. Potongan kode ini bisa langsung copas ke TypeScript Playground

Potongan kode ini melengkapi tulisan di lanjutkoding.com