Completed Challenges

Your TypeScript journey starts with these building blocks.

Type Aliases

You can create multiple names for the same type.

Literal Types

TypeScript can be more specific than string or number. It can remember literal values.

Index Signatures

Index signatures allow us to handle types where the properties are a non-specific literal value.

The `typeof` Operator

When you need to create a type from existing JavaScript values, typeof is the tool for the job.

Indexed Types

Some types can be indexed to lookup a particular value.

The `keyof` operator

keyof allows us to extract a union of another type's keys.

Generic Type Arguments

Generic types are like function arguments.

Generic Type Constraints

Generic type constraints allow us to restrict the possible types a generic type will accept.

Mapped Object Types

Mapping objects is a foundational skill that allows you to write type translation logic.

Generic Function Arguments

Give generic function types to your functions

Hello World

Hello, World!

In Type Challenges, we use the type system itself to do the assertion.

For this ch

Type Unions

Type unions are a powerful tool that allow you to create a type that's many values all at once.

Readonly

Implement the built-in Readonly<T> generic without using it.

Constructs a type with all proper

Tuple to Object

Given an array, transform it into an object type and the key/value must be in the provided array.

First of Array

Implement a generic First<T> that takes an Array T and returns its first element's type.

For

Length of Tuple

For given a tuple, you need create a generic Length, pick the length of the tuple

For example:

Exclude

Implement the built-in Exclude<T, U>

Exclude from T those types that are assignable to U

Awaited

If we have a type which is a wrapped type like Promise, how can we get the type which is inside th

If

Implement the util type If<C, T, F> which accepts condition C, a truthy value T, and a falsy

Concat

Implement the JavaScript Array.concat function in the type system. A type takes the two argument

Includes

Implement the JavaScript Array.includes function in the type system. A type takes the two argume

Push

Implement the generic version of Array.push

For example:


type Result = Push<

Unshift

Implement the type version of Array.unshift

For example:


type Result = Unshi

Parameters

Implement the built-in Parameters generic without using it.

For example:


const foo = (a

The `Pick` builtin

TypeScript ships with a Pick type. Learn how to make it yourself!

Get Return Type

Implement the built-in ReturnType<T> generic without using it.

For example


const fn = (v

Omit

Implement the built-in Omit<T, K> generic without using it.

Constructs a type by picking all pr

Readonly 2

Implement a generic MyReadonly2<T, K> which takes two type argument T and K.

K specify th

Deep Readonly

Implement a generic DeepReadonly<T> which make every parameter of an object - and its sub-object

Tuple to Union

Implement a generic TupleToUnion<T> which covers the values of a tuple to its values union.

For

Chainable Options

Chainable options are commonly used in Javascript. But when we switch to TypeScript, can you prope

Last of Array

TypeScript 4.0 is recommended in this challenge

Implement a generic Last<T> that takes an Arr

Pop

TypeScript 4.0 is recommended in this challenge

Implement a generic Pop<T> that takes an Arra

Promise.all

Type the function PromiseAll that accepts an array of PromiseLike objects, the returning value s

Type Lookup

Sometimes, you may want to look up a type in a union by its attributes.

In this challenge, we wou

Trim Left

Implement TrimLeft<T> which takes an exact string type and returns a new string with the whitesp

Trim

Implement Trim<T> which takes an exact string type and returns a new string with the whitespace

Capitalize

Implement Capitalize<T> which converts the first letter of a string to uppercase and leave the r

Absolute

Implement the Absolute type. A type that take string, number or bigint. The output should be a p

All

Returns true if all elements of the list are equal to the second parameter passed in, false if the

AnyOf

Implement Python liked any function in the type system. A type takes the Array and returns `true

Append Argument

For given function type Fn, and any type A (any in this context means we don't restrict the ty

Append to object

Implement a type that adds a new field to the interface. The type takes the three arguments. The o

BEM style string