Exclude type in Typescript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Exclude type example?

Consider the following TypeScript code using Exclude. What is the type of Result?

Typescript

type Letters = 'a' | 'b' | 'c' | 'd';
type Result = Exclude<Letters, 'a' | 'd'>;

// What is the type of Result?

A "b" | "c" | "d"

B "b" | "c"

C "a" | "b" | "c" | "d"

D "a" | "d"

💡 Hint

The Exclude type removes the types on the right from the union on the left.

The Exclude utility type removes 'a' and 'd' from the union 'a' | 'b' | 'c' | 'd', leaving 'b' | 'c'.

❓ Predict Output

intermediate

What does this Exclude type produce?

Given this code, what is the type of Filtered?

Typescript

type Status = 'success' | 'error' | 'loading';
type Filtered = Exclude<Status, 'loading'>;

A "success" | "error"

B "loading"

C "success" | "error" | "loading"

D never

💡 Hint

Exclude removes the specified type from the union.

Removing 'loading' from Status leaves 'success' | 'error'.

❓ Predict Output

advanced

What is the output of this Exclude with object keys?

What is the resulting type of KeysWithoutId?

Typescript

type Obj = { id: number; name: string; age: number };
type Keys = keyof Obj;
type KeysWithoutId = Exclude<Keys, 'id'>;

A "name" | "age"

B "id" | "name" | "age"

C "id"

D never

💡 Hint

Use keyof to get keys, then exclude 'id'.

keyof Obj is 'id' | 'name' | 'age'. Excluding 'id' leaves 'name' | 'age'.

❓ Predict Output

advanced

What error does this code raise?

What error will this code produce?

Typescript

type A = 'x' | 'y';
type B = Exclude<A, 'z'>;

const test: B = 'z';

A No error, assignment is valid.

B SyntaxError: Unexpected token

C Type '"z"' is not assignable to type '"x" | "y"'.

D TypeError: Exclude cannot exclude 'z'

💡 Hint

Check if the assigned value is part of the type after exclusion.

Since 'z' is not in 'x' | 'y', assigning 'z' to test causes a type error.

🧠 Conceptual

expert

How many items are in the resulting union type?

Given this code, how many string literal types remain in Remaining?

Typescript

type All = 'red' | 'green' | 'blue' | 'yellow' | 'black';
type Remove = 'green' | 'yellow' | 'white';
type Remaining = Exclude<All, Remove>;

A 2

B 4

C 5

D 3

💡 Hint

Count how many items from All are not in Remove.

Remove includes 'green' and 'yellow' which are removed from All. The remaining are 'red', 'blue', and 'black', so 3 items.