Recursive generic types in Typescript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a recursive generic type for a nested array.

Typescript

type NestedArray<T> = T | Array<[1]>;

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AT

BArray<T>

CNestedArray<T>

Dany

Attempts:

3 left

💡 Hint

Common Mistakes

Using T instead of the recursive type inside the array.

Using Array which does not allow nested arrays.

The type NestedArray is recursive because it refers to itself inside the array definition, allowing nested arrays of any depth.

2fill in blank

medium

Complete the code to define a recursive generic type for a tree node with children.

Typescript

type TreeNode<T> = { value: T; children?: Array<[1]> };

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Aany

BT

CArray<T>

DTreeNode<T>

Attempts:

3 left

💡 Hint

Common Mistakes

Using T instead of TreeNode for children.

Omitting the array wrapper for children.

The TreeNode type is recursive because the children property is an array of TreeNode itself, allowing nested tree structures.

3fill in blank

hard

Fix the error in the recursive generic type for a linked list node.

Typescript

type LinkedList<T> = { value: T; next: [1] | null };

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AT

BLinkedList<T>

CArray<T>

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Using T instead of LinkedList for next.

Using Array which is incorrect for linked list.

The next property should be either another LinkedList node or null, making the type recursive.

4fill in blank

hard

Fill both blanks to define a recursive generic type for a JSON value.

Typescript

type JSONValue = string | number | boolean | null | { [key: string]: [1] } | Array<[2]>;

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AJSONValue

Bany

Cunknown

Dobject

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'any' or 'unknown' which loses type safety.

Using different types for object values and array elements.

The JSONValue type is recursive because objects and arrays can contain other JSON values, including nested objects and arrays.

5fill in blank

hard

Fill all three blanks to define a recursive generic type for a nested dictionary with string keys.

Typescript

type NestedDict<T> = { [key: string]: T | [1]<T> | Array<[2]<T>> }; function processDict<T>(dict: [3]<T>) { /* ... */ }

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ANestedDict

BT

DArray

Attempts:

3 left

💡 Hint

Common Mistakes

Using T instead of NestedDict for nested dictionaries.

Using Array instead of NestedDict inside the array.

Mismatching the function parameter type.

The NestedDict type is recursive because dictionary values can be either the base type T, another nested dictionary, or an array of nested dictionaries. The function parameter uses the same recursive type.