export {}; declare global { type Maybe = T | null | undefined | []; type resModelOne = { status: number; message: string; postion: number; data: any[]; meta: null; user_id: number; } type resModelTwo = { status: number; message: string; postion: number; meta: null; _index: string; _id: string; _score: number; _source: {}; } type resModelThree = { status: number; message: string; postion: number; meta: null; took: number; timed_out: boolean; aggregations:[]; _shards: { total: number; successful: number; skipped: number; failed: number; }; hits: { total: { value: number; relation: string; }; max_score: null; hits: Maybe; }; } } // if no chapter found, undefined will return,else a chapter. // because of this, we need 'Maybe'. // const chapter : Maybe = course.chapters.find( // (chapter)=> chapter.slug === chapterSlug // );