Generic array syntax in Typescript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this TypeScript code using generic array syntax?

Consider the following TypeScript code snippet. What will be logged to the console?

Typescript

const numbers: Array<number> = [1, 2, 3];
const doubled = numbers.map(x => x * 2);
console.log(doubled);

A TypeError at runtime

B [2, 4, 6]

C [1, 2, 3]

D SyntaxError during compilation

💡 Hint

Think about what the map function does to each element in the array.

The map function applies the given function to each element of the array, doubling each number. So the output is [2, 4, 6].

❓ Predict Output

intermediate

What is the type of this generic array in TypeScript?

Given this declaration, what is the type of the variable 'words'?

Typescript

let words: Array<string> = ['hello', 'world'];

A Array of strings

B Array of numbers

C Tuple of strings

D Array of any type

💡 Hint

Look at the generic type inside the angle brackets.

The generic type Array means an array where every element is a string.

🔧 Debug

advanced

Why does this TypeScript code cause a compilation error?

Examine the code below. Why does it cause a TypeScript compilation error?

Typescript

const mixed: Array<number> = [1, 2, '3'];

A Because '3' is a string, not a number, violating the generic type Array<number>

B Because arrays cannot be declared with generic syntax

C Because the array is missing a type annotation

D Because the array is empty

💡 Hint

Check the types of all elements inside the array.

The array is declared to hold only numbers, but '3' is a string, causing a type mismatch error.

❓ Predict Output

advanced

What is the output of this TypeScript code using generic array syntax with union types?

What will be the output of this code snippet?

Typescript

const items: Array<number | string> = [1, 'two', 3];
const filtered = items.filter(item => typeof item === 'number');
console.log(filtered);

A ['two']

B [1, 'two', 3]

C [1, 3]

D TypeError at runtime

💡 Hint

The filter keeps only numbers from the array.

The filter function returns only elements whose type is 'number', so the output is [1, 3].

🧠 Conceptual

expert

How many elements are in the resulting array after this TypeScript code runs?

Consider this code snippet. How many elements does the 'result' array contain after execution?

Typescript

function createArray<T>(length: number, value: T): Array<T> {
  return new Array(length).fill(value);
}
const result = createArray<string>(3, 'hi');

A Undefined

B 1

C 0

D 3

💡 Hint

The fill method fills the array with the given value for the specified length.

The function creates an array of length 3, filled with the string 'hi', so the result has 3 elements.