Understanding TypeScript Utility Types: Omit, Pick, Exclude, and Extract

TypeScript provides powerful utility types to manipulate and transform existing types. Among them, Omit, Pick, Exclude, and Extract are commonly used for type operations. While they may seem similar, each serves a distinct purpose.

In this blog post, we’ll explore:

1. What each utility type does
2. Key differences between them
3. Practical use cases

1. Pick<Type, Keys> – Select Specific Properties

Pick creates a new type by selecting only the specified properties from an existing type.

Syntax:

Pick<Type, "key1" | "key2"> 

Example

interface User {

  id: number;

  name: string;

  email: string;

  age: number;

}

type UserBasicInfo = Pick<User, "name" | "email">;

// Equivalent to: { name: string; email: string; }

Use Case:

1. Extracting a subset of properties from a larger type (e.g., API response filtering).

2. Omit<Type, Keys> – Remove Specific Properties

Omit does the opposite of Pick—it removes specified properties from a type, keeping the rest.

Syntax:

Omit<Type, "key1" | "key2"> 

Example:

interface User {

  id: number;

  name: string;

  email: string;

  age: number;

}

type UserWithoutId = Omit<User, "id">;

// Equivalent to: { name: string; email: string; age: number; }

Use Case:

• Excluding sensitive fields (e.g., password, id) before sending data to a client.

3. Exclude<UnionType, ExcludedMembers> – Filter Union Types

Exclude removes specific members from a union type.

Syntax:

Exclude<UnionType, "value1" | "value2"> 

Example:

type Status = "pending" | "completed" | "failed";

type NonFailedStatus = Exclude<Status, "failed">;

// Equivalent to: "pending" | "completed"

Use Case:

• Narrowing down allowed values in a discriminated union.

4. Extract<UnionType, Match> – Keep Matching Union Members

Extract does the opposite of Exclude—it keeps only the matching members from a union.

Syntax:

Extract<UnionType, "value1" | "value2"> 

Example:

type Status = "pending" | "completed" | "failed";

type OnlyCompleted = Extract<Status, "completed">;

// Equivalent to: "completed"

Use Case:

• Extracting specific variants from a union (e.g., filtering valid statuses).

Key Differences Summary

Object types: Selects specific properties Omit

Object types: Removes specific properties Exclude

Union types: Removes matching members Extract

Union types: Keeps only matching members

When to Use Each?

• Use Pick/Omit when working with objects.
• Use Exclude/Extract when working with union types.

Example Combining Them:

type User = { id: number; name: string; role: "admin" | "user" };

type PublicUser = Omit<User, "id"> & { role: Extract<User["role"], "user"> };

// Result: { name: string; role: "user" }

Conclusion

Understanding these utility types helps in:

• Writing cleaner type definitions
• Reducing redundancy
• Improving type safety

By mastering Pick, Omit, Exclude, and Extract, you can manipulate TypeScript types more effectively.