Void type for functions in Typescript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a void function with console.log

What is the output of the following TypeScript code?

Typescript

function greet(): void {
  console.log('Hello!');
}

const result = greet();
console.log(result);

A undefined\nHello!

B Hello!\nvoid

C Hello!\nundefined

D Hello!

💡 Hint

Remember that functions with void return type do not return a value, so the result is undefined.

The function greet prints 'Hello!' to the console. Since it returns void, the variable result is undefined. So the console.log(result) prints 'undefined'.

🧠 Conceptual

intermediate

Understanding void return type in TypeScript

Which statement about the void return type in TypeScript functions is correct?

A A function with void return type can return undefined or no value at all.

B A function with void return type returns the string 'void' by default.

C A function with void return type must always return null explicitly.

D A function with void return type cannot return any value, not even undefined.

💡 Hint

Think about what happens when you omit a return statement in a void function.

In TypeScript, a function declared with void return type can either return nothing or return undefined explicitly. Returning other values causes an error.

🔧 Debug

advanced

Identify the error with void function return

What error will this TypeScript code produce?

Typescript

function calculate(): void {
  return 5;
}

A Type 'number' is not assignable to type 'void'.

B No error, function returns 5 correctly.

C SyntaxError: Unexpected return value.

D Runtime error: Cannot return value from void function.

💡 Hint

Check the return type and what is being returned.

A function declared with void return type cannot return a value other than undefined. Returning 5 causes a type error.

❓ Predict Output

advanced

Void function with callback parameter

What will be the output of this TypeScript code?

Typescript

function process(callback: () => void): void {
  console.log('Start');
  callback();
  console.log('End');
}

process(() => console.log('Inside callback'));

A Inside callback\nStart\nEnd

B Start\nInside callback\nEnd

C Start\nEnd\nInside callback

D Start\nEnd

💡 Hint

The callback is called between the two console.log statements.

The function prints 'Start', then calls the callback which prints 'Inside callback', then prints 'End'.

🧠 Conceptual

expert

Void type and async functions in TypeScript

Which statement about async functions with void return type in TypeScript is true?

A Declaring async functions with void return type causes a runtime error.

B Async functions cannot have void return type because they always return a Promise.

C Async functions with void return type return undefined immediately.

D An async function declared with void return type actually returns Promise<void>.

💡 Hint

Think about what async functions return in TypeScript.

Async functions always return a Promise. Declaring return type void means the Promise resolves with no value, so the actual return type is Promise.