Extract type in Typescript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to extract the type of elements from the array.

Typescript

type ElementType = Extract<[1], string[]>;

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Astring[]

Bnumber[]

Cboolean[]

Dany[]

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing a type that is not part of the union.

Confusing the order of types in Extract.

The Extract utility type extracts from the first type those types that are assignable to the second. Here, it extracts string[] from the union.

2fill in blank

medium

Complete the code to extract only the string literal types from the union.

Typescript

type OnlyStrings = Extract<'a' | 1 | true, [1]>;

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Anumber

Bboolean

Cstring

Dstring | number

Attempts:

3 left

💡 Hint

Common Mistakes

Using a union type instead of a single type.

Using the wrong primitive type.

The Extract type keeps only the types assignable to string, so only the string literals remain.

3fill in blank

hard

Fix the error in the code to correctly extract the function type from the union.

Typescript

type FuncType = Extract<() => void | string, [1]>;

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Astring

BFunction

Cvoid

D() => void

Attempts:

3 left

💡 Hint

Common Mistakes

Using Function which is too broad.

Extracting the wrong type from the union.

The Extract type extracts the function type () => void from the union.

4fill in blank

hard

Fill both blanks to extract only the number types from the union and assign it to the variable.

Typescript

type NumbersOnly = Extract<[1], [2]>;

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A'a' | 1 | 2 | true

Bnumber

Cstring

Dboolean

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the order of the types in Extract.

Using the wrong type to extract.

The first blank is the union type containing strings, numbers, and booleans. The second blank is number to extract only number types.

5fill in blank

hard

Fill all three blanks to extract the types assignable to string or boolean from the union.

Typescript

type Extracted = Extract<[1], [2] | [3]>;

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A'hello' | 42 | false | true

Bstring

Cboolean

Dnumber

Attempts:

3 left

💡 Hint

Common Mistakes

Using number instead of boolean.

Not using a union type in the second argument.

The first blank is the union type with string, number, and boolean literals. The second and third blanks are string and boolean to extract those types.