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TypeScript Academy · Lesson

Record: Mapping Keys to Value Types

Build dictionary-like types with Record .

Lesson 3 of 413 steps

Record: Mapping Keys to Value Types is a free TypeScript Academy lesson on CoddyKit. This is lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the TypeScript Academy learning path, and your progress syncs across the web and the CoddyKit app. The TypeScript Academy course includes 4 lessons in total.

Welcome

Record creates an object type with specific keys K and a uniform value type V. It replaces manually typing every key in dictionary-like structures.

Basic Record Syntax

Pass a key type and value type to Record.
type Roles = Record<'admin' | 'user' | 'guest', boolean>;
const access: Roles = { admin: true, user: true, guest: false };

Record with string Keys

Use `string` as the key type for a general dictionary.
const headers: Record<string, string> = {
  'content-type': 'application/json',
  'authorization': 'Bearer token'
};

Record for Lookup Tables

Record is ideal for lookup tables where you map IDs or codes to values.
const statusLabels: Record<number, string> = {
  200: 'OK',
  404: 'Not Found',
  500: 'Server Error'
};

How Record Is Implemented

Record is a mapped type over the key union.
type Record<K extends string | number | symbol, V> = { [P in K]: V };

Record vs Index Signature

Record is equivalent to `{ [key: string]: V }` but is more readable and composable.
// Equivalent:
type A = Record<string, number>;
type B = { [key: string]: number };

Record with Union Values

The value type can be a union or complex type.
type Config = Record<'development' | 'staging' | 'production', { url: string; debug: boolean }>;

Partial Record

Combine with Partial to allow not all keys to be present.
type OptionalConfig = Partial<Record<'debug' | 'verbose' | 'trace', boolean>>;

Readonly Record

Combine with Readonly to prevent changes.
const CODES: Readonly<Record<string, number>> = { A: 1, B: 2 };

Record for Grouping

Use Record to group items by a category key.
function groupBy<T>(items: T[], key: keyof T): Record<string, T[]> {
  return items.reduce((acc, item) => {
    const k = String(item[key]);
    (acc[k] ??= []).push(item);
    return acc;
  }, {} as Record<string, T[]>);
}

Record with Enum Keys

Enum values work as Record keys.
enum Color { Red = 'RED', Green = 'GREEN', Blue = 'BLUE' }
const hexCodes: Record<Color, string> = {
  [Color.Red]: '#FF0000',
  [Color.Green]: '#00FF00',
  [Color.Blue]: '#0000FF',
};

Quick Check

What does `Record<'a' | 'b', number>` produce?
Answer it in the interactive lesson

Recap

Record creates a typed dictionary with specific keys and uniform value types. Use it for lookup tables, configuration maps, and groupBy results. Combine with Partial and Readonly for more control.
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Frequently Asked Questions

Is the “Record: Mapping Keys to Value Types” lesson free?

Yes — the full text of “Record: Mapping Keys to Value Types” is free to read here on the web. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the TypeScript Academy course, upgrade to CoddyKit PRO. The TypeScript Academy course includes 4 lessons in total.

What will I learn in “Record: Mapping Keys to Value Types”?

Build dictionary-like types with Record . You practise TypeScript Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start TypeScript Academy?

No prior experience is required. TypeScript Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 3 of 4.

How long does the “Record: Mapping Keys to Value Types” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this TypeScript Academy lesson?

Yes. Every TypeScript Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. Partial and Required: Toggling Optionality
  2. Pick and Omit: Selecting Properties
  3. Record: Mapping Keys to Value Types
  4. Readonly, Exclude, Extract, NonNullable
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