What types exist only at compile time in Typescript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a type alias in TypeScript.

Typescript

type Name = [1];

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Aboolean

B"string"

Cnumber

Dstring

Attempts:

3 left

💡 Hint

Common Mistakes

Putting quotes around type keywords like "string" instead of using string.

Using values instead of type keywords.

In TypeScript, string is a type keyword used only at compile time to describe the type of a variable.

2fill in blank

medium

Complete the code to define an interface in TypeScript.

Typescript

interface Person { name: [1]; age: number; }

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

A"string"

Bboolean

Cstring

Dnumber

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around string type.

Using number or boolean instead of string for name.

The string type describes text data and exists only at compile time in TypeScript.

3fill in blank

hard

Fix the error in this type assertion that uses a compile-time only type.

Typescript

const value = "hello" as [1];

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

AString

Bstring

C"string"

Dnumber

Attempts:

3 left

💡 Hint

Common Mistakes

Using quoted types like "string" in assertions.

Using the boxed type String instead of string.

Type assertions use compile-time types like string without quotes.

4fill in blank

hard

Fill both blanks to create a mapped type that exists only at compile time.

Typescript

type Readonly[1]<[2]> = { readonly [K in keyof [2]]: [2][K] };

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AProps

BT

CU

DV

Attempts:

3 left

💡 Hint

Common Mistakes

Using values instead of type parameter names.

Mixing up the generic parameter name and the new type name.

This mapped type creates a readonly version of a generic type T. Both Props and T are compile-time only types.

5fill in blank

hard

Fill all three blanks to define a conditional type that exists only at compile time.

Typescript

type IsString[1]<[2]> = [2] extends string ? true : [3];

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

ACheck

BT

Cfalse

Dboolean

Attempts:

3 left

💡 Hint

Common Mistakes

Using values instead of type parameter names.

Using boolean instead of false in the false branch.

This conditional type checks if T is string. It returns true or false, all compile-time types.