Tuple type definition in Typescript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this tuple length check?

Consider this TypeScript code that defines a tuple and checks its length.
What will be the output when this code runs?

Typescript

const myTuple: [string, number, boolean] = ['hello', 42, true];
console.log(myTuple.length);

A 3

B 2

C Error: Tuple length not accessible

D undefined

💡 Hint

Remember tuples are fixed-length arrays in TypeScript.

The tuple has exactly three elements, so its length property is 3.

❓ Predict Output

intermediate

What is the output when accessing a tuple element?

Given this tuple definition and access, what will be printed?

Typescript

const coords: [number, number] = [10, 20];
console.log(coords[1]);

A undefined

B 10

C 20

D Error: Index out of bounds

💡 Hint

Tuple elements are accessed by zero-based index.

coords[1] accesses the second element, which is 20.

🔧 Debug

advanced

What error does this tuple assignment cause?

This code tries to assign a tuple to a variable. What error will TypeScript report?

Typescript

let user: [string, number];
user = ['Alice', '25'];

A Tuple must have exactly 3 elements.

B No error, assignment is valid.

C Type 'number' is not assignable to type 'string'.

D Type 'string' is not assignable to type 'number'.

💡 Hint

Check the types of each tuple element carefully.

The second element should be a number, but '25' is a string.

📝 Syntax

advanced

Which option correctly defines a tuple type with optional elements?

Which of these tuple type definitions is valid TypeScript syntax for a tuple with an optional boolean as the third element?

A type MyTuple = [string, number?, boolean];

B type MyTuple = [string, number, boolean?];

C type MyTuple = [string?, number, boolean];

D type MyTuple = [string, number, ?boolean];

💡 Hint

Optional elements in tuples use a question mark after the type.

Only option B correctly places the question mark after the type to mark the third element optional.

🚀 Application

expert

What is the type of the variable 'result' after this tuple manipulation?

Given this TypeScript code, what is the type of 'result'?

Typescript

const data: [number, string, boolean] = [1, 'ok', true];
const result = data.slice(0, 2);

A Array<number | string>

B [number, string]

C [number, string, boolean]

D Array<number | string | boolean>

💡 Hint

Array.slice returns a new array, not a tuple.

The slice method returns a normal array with elements of the tuple types included, so the type is Array.