Utility Types in TypeScript

Welcome! In this guide, we’ll learn about Utility Types in TypeScript. These built-in types help you manipulate and transform other types, making your code cleaner and more manageable. Let’s explore how they work!

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What Are Utility Types?

Utility types in TypeScript are pre-defined types that allow you to quickly modify or extract information from other types. They save you time by automating common tasks like making fields optional, readonly, or picking specific properties from an object.

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Commonly Used Utility Types

Let’s look at some of the most popular utility types and how they can be useful.

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1. Partial

Converts all properties of a type to optional.

type User = {
  id: number;
  name: string;
  email: string;
};

const updateUser = (user: Partial<User>) => {
  console.log(user);
};

updateUser({ name: "Saurabh" }); // ✅ Valid, only name provided

Use Case :

When updating part of an object without requiring all fields.

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2. Required

Makes all properties required (opposite of Partial).

type User = {
  id?: number;
  name?: string;
  email?: string;
};

const createUser = (user: Required<User>) => {
  console.log(user);
};

createUser({ id: 1, name: "Saurabh", email: "test@example.com" }); // ✅ Valid

Use Case :

When you need to ensure all properties are present.

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3. Readonly

Makes all properties read-only, preventing them from being modified.

type User = {
  id: number;
  name: string;
};

const user: Readonly<User> = { id: 1, name: "Saurabh" };
// user.id = 2; // ❌ Error: Cannot assign to 'id' because it is read-only

Use Case :

When you want to create immutable objects.

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4. Pick

Selects a subset of properties from a type.

type User = {
  id: number;
  name: string;
  email: string;
};

type UserPreview = Pick<User, "id" | "name">;

const user: UserPreview = { id: 1, name: "Saurabh" };
console.log(user);

Use Case :

When you need only specific fields from a type.

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5. Omit

Removes certain properties from a type.

type User = {
  id: number;
  name: string;
  email: string;
};

type UserWithoutEmail = Omit<User, "email">;

const user: UserWithoutEmail = { id: 1, name: "Saurabh" };
console.log(user);

Use Case :

When you want to exclude some properties from an object type.

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6. Record

Creates a type with a fixed set of keys and values.

type Role = "admin" | "user" | "guest";

const permissions: Record<Role, string[]> = {
  admin: ["read", "write", "delete"],
  user: ["read", "write"],
  guest: ["read"],
};

console.log(permissions);

Use Case :

When you need to map keys to specific values.

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7. Exclude

Removes specific types from a union.

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

type NonPendingStatus = Exclude<Status, "pending">;

let status: NonPendingStatus = "success"; // ✅ Valid
// status = "pending"; // ❌ Error: Type '"pending"' is not assignable

Use Case:

When you want to exclude specific values from a union type.

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8. Extract

Extracts only the matching types from a union.

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

type OnlyPending = Extract<Status, "pending">;

let status: OnlyPending = "pending"; // ✅ Valid

Use Case:

When you need to filter out only certain types from a union.

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9. NonNullable

Removes null and undefined from a type.

type User = {
  id: number | null;
  name?: string;
};

type NonNullableId = NonNullable<User["id"]>;

let id: NonNullableId = 123; // ✅ Valid
// id = null; // ❌ Error: 'null' is not assignable

Use Case :

When you want to make sure a value is neither null nor undefined.

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💡 Conclusion

Utility types in TypeScript make working with types much easier by helping you modify and reuse them effectively. They improve your code’s clarity and reduce boilerplate.

Summary of Utility Types:

• Partial: Makes fields optional.
• Required: Makes fields required.
• Readonly: Makes fields read-only.
• Pick: Selects specific fields.
• Omit: Excludes specific fields.
• Record: Maps keys to values.
• Exclude: Removes types from unions.
• Extract: Extracts matching types.
• NonNullable: Removes null and undefined.

Use these types wisely to write cleaner, safer, and more efficient TypeScript code!

Happy coding with Typescript! 🎉

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