Async function syntax in Javascript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of an async function returning a value

What is the output of this code when run in a modern JavaScript environment?

Javascript

async function greet() {
  return 'Hello!';
}

greet().then(console.log);

A Hello!

B Promise { 'Hello!' }

C SyntaxError

D undefined

💡 Hint

Remember that async functions always return a Promise, but .then unwraps the value.

The async function greet returns a Promise that resolves to 'Hello!'. Using .then(console.log) prints the resolved value 'Hello!'.

❓ Predict Output

intermediate

Output of an async function with await

What will this code output to the console?

Javascript

async function getNumber() {
  const num = await Promise.resolve(42);
  return num;
}

getNumber().then(console.log);

A 42

B Promise { 42 }

C undefined

D TypeError

💡 Hint

The await keyword unwraps the Promise's resolved value.

The await pauses until the Promise resolves to 42, then returns 42. The .then logs 42.

❓ Predict Output

advanced

Error when missing async keyword

What error does this code produce?

Javascript

function fetchData() {
  await Promise.resolve('data');
}

fetchData();

A ReferenceError

B No error, runs fine

C TypeError

D SyntaxError

💡 Hint

await can only be used inside async functions.

Using await outside an async function causes a SyntaxError.

❓ Predict Output

advanced

Return value of an async arrow function

What is the output of this code?

Javascript

const asyncArrow = async () => 10;

asyncArrow().then(console.log);

A SyntaxError

B Promise { 10 }

C 10

D undefined

💡 Hint

Async arrow functions return Promises resolved with the returned value.

The async arrow function returns a Promise resolved with 10. The .then logs 10.

🧠 Conceptual

expert

Behavior of async function without await

What is the value of variable result after running this code?

Javascript

async function noAwait() {
  return 5;
}

const result = noAwait();

A 5

B Promise { 5 }

C undefined

D TypeError

💡 Hint

Async functions always return a Promise, even if no await is used.

The function noAwait returns a Promise resolved with 5. So result is a Promise object.