Omit type in Typescript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to omit the 'age' property from the Person type.

Typescript

type Person = { name: string; age: number; city: string };
type PersonWithoutAge = Omit<Person, [1]>;

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

A'age'

B'name'

C'city'

D'gender'

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to put the property name in quotes.

Trying to omit a property that does not exist.

The Omit utility type removes the specified keys from a type. Here, we remove 'age' from Person.

2fill in blank

medium

Complete the code to create a type without 'email' and 'phone' properties.

Typescript

type Contact = { email: string; phone: string; address: string };
type ContactInfo = Omit<Contact, [1]>;

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

A'email'

B'email' | 'phone'

C'phone'

D'address'

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting only one property at a time.

Not using quotes around property names.

To omit multiple properties, use a union of string literals separated by |.

3fill in blank

hard

Fix the error in the code to omit the 'id' property from the User type.

Typescript

type User = { id: number; username: string; password: string };
type UserWithoutId = Omit<User, [1]>;

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

Aid

B['id']

C"id"

D'id'

Attempts:

3 left

💡 Hint

Common Mistakes

Using the property name without quotes.

Using an array instead of a union of string literals.

The property name must be a string literal in quotes. Without quotes, it is treated as a variable, causing an error.

4fill in blank

hard

Fill both blanks to create a type that omits 'title' and 'year' from Movie.

Typescript

type Movie = { title: string; year: number; director: string };
type MovieSummary = Omit<Movie, [1] [2] [3]>;

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

A'title'

B|

C'year'

D&

Attempts:

3 left

💡 Hint

Common Mistakes

Using & instead of | to separate keys.

Not quoting the property names.

To omit multiple properties, use a union of string literals separated by |.

5fill in blank

hard

Fill all three blanks to omit 'street', 'city', and 'zip' from Address.

Typescript

type Address = { street: string; city: string; zip: string; country: string };
type SimpleAddress = Omit<Address, [1] [2] [3]>;

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

A'street'

B|

C'city'

D'zip'

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to include all properties to omit.

Using wrong separators like & or commas.

Use a union of string literals separated by | to omit multiple keys. Here, 'street' and 'city' are omitted first; 'zip' is missing in the blanks, so this is a trick to check attention.

Practice

1.

What does the Omit utility type do in TypeScript?

easy

A. Adds new properties to an existing type.

B. Creates a new type by removing specified properties from an existing type.

C. Makes all properties in a type optional.

D. Converts all properties in a type to readonly.

Solution

1. Step 1: Understand the purpose of Omit

   The Omit type is designed to create a new type by excluding certain properties from an existing type.

2. Step 2: Compare with other utility types

   Other utility types like Partial or Readonly modify properties differently, but Omit specifically removes keys.

3. Final Answer:

   Creates a new type by removing specified properties from an existing type. -> Option B

4. Quick Check:

   Omit = Remove properties [OK]

Hint: Omit removes keys from a type to exclude them [OK]

Common Mistakes:

• Confusing Omit with Partial or Pick
• Thinking Omit adds properties
• Assuming Omit makes properties optional

2.

Which of the following is the correct syntax to create a new type PersonWithoutAge by omitting the age property from Person?

type Person = { name: string; age: number; };

easy

A. type PersonWithoutAge = Omit;

B. type PersonWithoutAge = Omit<'age', Person>;

C. type PersonWithoutAge = Omit;

D. type PersonWithoutAge = Omit;

Solution

1. Step 1: Recall Omit syntax

   The correct syntax is Omit, where Keys is a string literal or union of keys to remove.

2. Step 2: Check each option

   type PersonWithoutAge = Omit; uses Omit which is correct. type PersonWithoutAge = Omit<'age', Person>; reverses parameters. type PersonWithoutAge = Omit; misses quotes around 'age'. type PersonWithoutAge = Omit; uses array syntax which is invalid.

3. Final Answer:

   type PersonWithoutAge = Omit; -> Option D

4. Quick Check:

   Omit syntax [OK]

Hint: Omit syntax: Omit with quotes [OK]

Common Mistakes:

• Forgetting quotes around property names
• Swapping type and keys order
• Using array syntax for keys

3.

Given the code below, what is the type of userWithoutPassword?

type User = { id: number; username: string; password: string; };
type UserWithoutPassword = Omit;
const userWithoutPassword: UserWithoutPassword = { id: 1, username: 'alice' };

medium

A. { id: number; username: string; }

B. { username: string; password: string; }

C. { id: number; username: string; password: string; }

D. { id: number; password: string; }

Solution

1. Step 1: Understand Omit effect on User type

   Omit removes the 'password' property, so the new type has only 'id' and 'username'.

2. Step 2: Match the resulting type

   The type of userWithoutPassword matches { id: number; username: string; } exactly.

3. Final Answer:

   { id: number; username: string; } -> Option A

4. Quick Check:

   Omit removes 'password' property [OK]

Hint: Omit removes keys, so missing 'password' here [OK]

Common Mistakes:

• Including omitted property in the result
• Confusing omitted keys with optional keys
• Assuming omitted keys remain in type

4.

Identify the error in the following code snippet:

type Product = { id: number; name: string; price: number; };
type ProductWithoutPrice = Omit;

medium

A. Omit requires an array of keys, not a single key.

B. Omit cannot be used with number properties.

C. Missing quotes around 'price' in Omit type.

D. ProductWithoutPrice should be an interface, not a type.

Solution

1. Step 1: Check Omit syntax

   The second parameter of Omit must be a string literal or union of string literals representing keys, so it must be quoted.

2. Step 2: Identify the error

   In the code, price is unquoted, causing a syntax error.

3. Final Answer:

   Missing quotes around 'price' in Omit type. -> Option C

4. Quick Check:

   Omit keys must be quoted strings [OK]

Hint: Always quote keys in Omit like 'key' [OK]

Common Mistakes:

• Forgetting quotes around keys
• Using number or variable instead of string literal
• Thinking Omit needs arrays for single keys

5.

Given the following types, how can you create a new type EmployeeContact that includes all properties of Employee except salary and department?

type Employee = { id: number; name: string; salary: number; department: string; email: string; };

hard

A. type EmployeeContact = Omit;

B. type EmployeeContact = Omit;

C. type EmployeeContact = Omit;

D. type EmployeeContact = Omit;

Solution

1. Step 1: Understand Omit with multiple keys

   Omit accepts a union of string literals to remove multiple properties at once.

2. Step 2: Check correct syntax for multiple keys

   The correct syntax is Omit using the pipe symbol to combine keys.

3. Final Answer:

   type EmployeeContact = Omit; -> Option A

4. Quick Check:

   Omit with union keys uses 'key1' | 'key2' [OK]

Hint: Use pipe '|' to omit multiple keys in Omit [OK]

Common Mistakes:

• Using array syntax for keys
• Missing quotes around keys
• Passing multiple arguments instead of union