Required type in Typescript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to make all properties required in the type.

Typescript

type User = {
  name?: string;
  age?: number;
};
type RequiredUser = [1]<User>;

Drag options to blanks, or click blank then click option'

APartial

BPick

CReadonly

DRequired

Attempts:

3 left

💡 Hint

Common Mistakes

Using Partial instead of Required

Using Readonly which only makes properties readonly

Using Pick which selects properties but does not change optionality

The Required utility type makes all properties of a type required (non-optional).

2fill in blank

medium

Complete the code to make all properties required in the interface.

Typescript

interface Product {
  id?: number;
  name?: string;
}
type CompleteProduct = [1]<Product>;

Drag options to blanks, or click blank then click option'

ARequired

BPartial

CReadonly

DOmit

Attempts:

3 left

💡 Hint

Common Mistakes

Using Omit which removes properties

Using Partial which makes properties optional

Using Readonly which only affects mutability

The Required type converts all optional properties to required.

3fill in blank

hard

Fix the error by completing the code to make all properties required in the type alias.

Typescript

type Config = {
  debug?: boolean;
  verbose?: boolean;
};
type FullConfig = [1]<Config>;

const config: FullConfig = {
  debug: true,
  verbose: false
};

Drag options to blanks, or click blank then click option'

ARequired

BPartial

CReadonly

DPick

Attempts:

3 left

💡 Hint

Common Mistakes

Using Partial which makes properties optional

Using Readonly which does not affect optionality

Using Pick which selects properties but does not change optionality

Using Required ensures all properties must be provided, fixing the error.

4fill in blank

hard

Fill both blanks to create a required type from a partial type and assign a value.

Typescript

type Settings = [1]<{
  theme?: string;
  layout?: string;
}>;

const defaultSettings: Settings = {
  theme: 'dark',
  [2]: 'grid'
};

Drag options to blanks, or click blank then click option'

ARequired

Blayout

Ctheme

DPartial

Attempts:

3 left

💡 Hint

Common Mistakes

Using Partial instead of Required

Assigning a property name that does not exist

Forgetting to assign all required properties

Use Required to make all properties required, then assign layout property.

5fill in blank

hard

Fill all three blanks to create a required type from an interface, assign properties, and use a function parameter.

Typescript

interface Profile {
  username?: string;
  email?: string;
  age?: number;
}

type CompleteProfile = [1]<Profile>;

function printProfile(profile: [2]) {
  console.log(`User: ${profile.username}, Email: ${profile.email}, Age: ${profile.age}`);
}

const user: CompleteProfile = {
  username: 'alice',
  [3]: '[e-mail]',
  age: 30
};

printProfile(user);

Drag options to blanks, or click blank then click option'

ARequired

BCompleteProfile

Cemail

DProfile

Attempts:

3 left

💡 Hint

Common Mistakes

Using Profile instead of CompleteProfile in function parameter

Forgetting to assign the email property

Using Partial instead of Required

Use Required to make all properties required, then use the new type CompleteProfile as function parameter type, and assign the email property.

Practice

1. What does the Required utility type do in TypeScript?

easy

A. Makes all properties of a type optional

B. Makes all properties of a type mandatory

C. Removes all properties from a type

D. Allows properties to be undefined

Solution

1. Step 1: Understand the purpose of Required

   The Required utility type transforms all optional properties of a type into required ones.

2. Step 2: Compare options with definition

   Only Makes all properties of a type mandatory correctly states that Required makes all properties mandatory.

3. Final Answer:

   Makes all properties of a type mandatory -> Option B

4. Quick Check:

   Required = all mandatory [OK]

Hint: Remember: Required means no optional properties allowed [OK]

Common Mistakes:

• Confusing Required with Partial (which makes properties optional)
• Thinking Required removes properties
• Assuming Required allows undefined values

2. Which of the following is the correct syntax to make all properties of interface User required using Required?

easy

A. type CompleteUser = Required<User>;

B. type CompleteUser = Partial<User>;

C. type CompleteUser = Optional<User>;

D. type CompleteUser = Readonly<User>;

Solution

1. Step 1: Recall the syntax of Required

   The correct syntax to apply Required is Required<TypeName>.

2. Step 2: Match options with syntax

   type CompleteUser = Required<User>; uses Required<User> correctly. Others use different utility types or incorrect names.

3. Final Answer:

   type CompleteUser = Required<User>; -> Option A

4. Quick Check:

   Use Required<Type> for all mandatory props [OK]

Hint: Use Required<Type> exactly to enforce all properties [OK]

Common Mistakes:

• Using Partial instead of Required
• Typing Optional which doesn't exist in TypeScript
• Confusing Readonly with Required

3. Given the interface and type below, what is the type of user2?

interface User {
  name?: string;
  age?: number;
}

const user2: Required<User> = {
  name: "Alice",
  age: 30
};

medium

A. An object where name and age are required

B. An object where name and age are optional

C. An object where only name is required

D. An object where age is optional

Solution

1. Step 1: Analyze the interface User

   Both name and age are optional properties in User.

2. Step 2: Understand Required<User>

   The Required utility makes all optional properties required, so name and age must be present.

3. Final Answer:

   An object where name and age are required -> Option A

4. Quick Check:

   Required<User> = all required props [OK]

Hint: Required makes all optional props mandatory [OK]

Common Mistakes:

• Thinking optional props stay optional
• Assuming only some props become required
• Confusing Required with Partial

4. What is the error in this code snippet?

interface Product {
  id?: number;
  name?: string;
}

const product: Required<Product> = {
  id: 101
};

medium

A. Cannot assign object to interface Product

B. Type 'number' is not assignable to 'string'

C. No error, code is correct

D. Missing property 'name' in object

Solution

1. Step 1: Check properties in Required<Product>

   Both id and name are required because of Required.

2. Step 2: Compare object properties with interface

   The object only has id, missing name, causing a TypeScript error.

3. Final Answer:

   Missing property 'name' in object -> Option D

4. Quick Check:

   Required means all props must be present [OK]

Hint: Check all required props are present in object [OK]

Common Mistakes:

• Ignoring missing required properties
• Thinking optional props remain optional
• Assuming partial object assignment is allowed

5. You have a type with some optional properties:

type Config = {
  host?: string;
  port?: number;
  secure?: boolean;
};

You want to create a new type FullConfig where all properties are required, but also want to add a new property timeout which is required. Which is the correct way to do this?

hard

A. type FullConfig = Partial<Config> & { timeout?: number };

B. type FullConfig = Required<Config> & { timeout?: number };

C. type FullConfig = Required<Config> & { timeout: number };

D. type FullConfig = Config & { timeout: number };

Solution

1. Step 1: Make all Config properties required

   Use Required<Config> to make host, port, and secure mandatory.

2. Step 2: Add new required property timeout

   Use intersection & with { timeout: number } to add a required timeout property.

3. Final Answer:

   type FullConfig = Required<Config> & { timeout: number }; -> Option C

4. Quick Check:

   Required + intersection adds required props [OK]

Hint: Combine Required<Type> & { newProp: type } for extra required props [OK]

Common Mistakes:

• Using Partial instead of Required
• Making new property optional when it should be required
• Not combining types correctly