TypeScript Record Utility Type Explained

Welcome back! I am Mihir, and in this lesson we will learn the Record utility type in TypeScript.

Record<K, T> creates an object type where keys are K and values are T.

Basic Record Example

type Scores = Record<string, number>;

const scores: Scores = {
  mihir: 95,
  alex: 88,
};

This means every string key has a number value.

Fixed Keys with Record

type Role = "admin" | "editor" | "viewer";

type RolePermissions = Record<Role, string[]>;

Usage:

const permissions: RolePermissions = {
  admin: ["create", "read", "update", "delete"],
  editor: ["read", "update"],
  viewer: ["read"],
};

All roles must be present.

Missing Keys Cause Errors

Invalid:

const permissions: RolePermissions = {
  admin: ["create"],
  editor: ["read"],
};

viewer is missing.

Value Types Are Checked

Invalid:

const permissions: RolePermissions = {
  admin: "all",
  editor: ["read"],
  viewer: ["read"],
};

Each value must be string[].

Record for Lookup Objects

type Status = "success" | "error" | "loading";

const statusLabels: Record<Status, string> = {
  success: "Success",
  error: "Something went wrong",
  loading: "Loading...",
};

This is cleaner than a long chain of if statements for simple lookup values.

Record vs Index Signature

Index signature:

type Scores = {
  [name: string]: number;
};

Record:

type Scores = Record<string, number>;

They are similar for simple dictionaries. Record is shorter and works nicely with unions of fixed keys.

Quick Recap

• Record<K, T> creates an object map.
• K is the key type.
• T is the value type.
• It is useful for dictionaries and lookup objects.
• With union keys, Record requires every key to exist.

Next up, we will learn Exclude and Extract →.