Careeroza

Record

Record of Keys to Values

Record<K, V> is an object type whose keys are K and values are V. With a literal union for K, every key is required, which makes lookup tables complete.

Example

type Category = "electronics" | "books" | "fashion" | "grocery";

const gstRate: Record<Category, number> = {
  electronics: 18,
  books: 0,
  fashion: 12,
  grocery: 5,
};

const countByCategory: Record<string, number> = {};
for (const c of ["books", "fashion", "books"]) {
  countByCategory[c] = (countByCategory[c] ?? 0) + 1;
}

console.log(gstRate.fashion, gstRate.books);
console.log(countByCategory);

Output

12 0
{ books: 2, fashion: 1 }

Missing a Key

Example

Leaving out grocery is an error (TS2741).

type Category = "electronics" | "books" | "grocery";
const gstRate: Record<Category, number> = { electronics: 18, books: 0 };

Compiler output (tsc)

Line 2: error TS2741: Property 'grocery' is missing in type '{ electronics: number; books: number; }' but required in type 'Record<Category, number>'.