Generic functions with arrays in Typescript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a generic function that returns the first element of an array.

Typescript

function firstElement<[1]>(arr: [1][]): [1] {
  return arr[0];
}

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

AT

BK

CV

DU

Attempts:

3 left

💡 Hint

Common Mistakes

Using a lowercase letter for the generic type parameter.

Using different type parameters for the array and return type.

The generic type parameter T is commonly used to represent any type. Here, it allows the function to accept an array of any type and return an element of that same type.

2fill in blank

medium

Complete the code to create a generic function that returns the length of any array.

Typescript

function getLength<[1]>(items: [1][]): number {
  return items.length;
}

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AU

BY

CX

DT

Attempts:

3 left

💡 Hint

Common Mistakes

Using a generic type parameter that does not match the array element type.

Forgetting to specify the generic type parameter in the function signature.

The generic type parameter T is used here to represent the type of elements in the array. The function returns the length of the array regardless of element type.

3fill in blank

hard

Fix the error in the generic function that swaps the first and last elements of an array.

Typescript

function swapFirstLast<[1]>(arr: [1][]): [1][] {
  const temp = arr[0];
  arr[0] = arr[arr.length - 1];
  arr[arr.length - 1] = temp;
  return arr;
}

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

AV

BU

CT

DW

Attempts:

3 left

💡 Hint

Common Mistakes

Using different generic type parameters in the function signature and parameter.

Not declaring the generic type parameter at all.

The generic type parameter T is used consistently to indicate the type of elements in the array. This ensures the function works for any array type.

4fill in blank

hard

Fill both blanks to create a generic function that filters an array based on a condition.

Typescript

function filterArray<[1]>(arr: [1][], predicate: (item: [2]) => boolean): [1][] {
  return arr.filter(predicate);
}

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AT

BU

DV

Attempts:

3 left

💡 Hint

Common Mistakes

Using different generic type parameters for the array and predicate argument.

Not using a generic type parameter at all.

The generic type parameter T is used for both the array element type and the predicate function parameter to ensure type consistency.

5fill in blank

hard

Fill all three blanks to create a generic function that maps an array to another array using a transform function.

Typescript

function mapArray<[1] , [2]>(arr: [1][], transform: (item: [3]) => [2]): [2][] {
  return arr.map(transform);
}

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

AT

BU

DV

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same generic type parameter for input and output types.

Not declaring both generic type parameters.

The generic type parameters T and U represent the input and output types respectively. The function uses these to type the array and transform function correctly.