Return inside loops in Javascript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this code with return inside a for loop?

Look at the function below. What will testReturn() output when called?

Javascript

function testReturn() {
  for (let i = 0; i < 5; i++) {
    if (i === 2) {
      return i;
    }
  }
  return -1;
}
console.log(testReturn());

A 4

B 2

C 0

D -1

💡 Hint

Remember that return immediately exits the function.

The function loops from 0 to 4. When i is 2, it returns 2 immediately, so the loop and function stop.

❓ Predict Output

intermediate

What does this function return?

What will the function findFirstEven return?

Javascript

function findFirstEven(arr) {
  for (const num of arr) {
    if (num % 2 === 0) {
      return num;
    }
  }
  return null;
}
console.log(findFirstEven([1, 3, 5, 6, 8]));

A 1

B 3

C null

D 6

💡 Hint

The function returns the first even number it finds.

The loop checks each number. The first even number is 6, so it returns 6 immediately.

❓ Predict Output

advanced

What is the output of this nested loop with return?

What will this function output when called?

Javascript

function nestedReturn() {
  for (let i = 0; i < 3; i++) {
    for (let j = 0; j < 3; j++) {
      if (i + j === 3) {
        return i * j;
      }
    }
  }
  return -1;
}
console.log(nestedReturn());

A 2

B 3

C 0

D -1

💡 Hint

Check when i + j === 3 happens first and what i * j is then.

The first time i + j === 3 is true is when i=1 and j=2. Then i * j = 2. Since j only goes up to 2, this is the first valid pair.

❓ Predict Output

advanced

What happens if return is inside a forEach loop?

What will this code output?

Javascript

function testForEach() {
  [1, 2, 3].forEach(num => {
    if (num === 2) {
      return num;
    }
  });
  return 'done';
}
console.log(testForEach());

A 2

B TypeError

C done

D undefined

💡 Hint

Remember that return inside forEach only exits the callback, not the outer function.

The return inside forEach stops the callback for that iteration only. The outer function continues and returns 'done'.

🧠 Conceptual

expert

Why does return inside a loop behave differently in forEach vs for-of?

Consider these two functions:

function a(arr) {
  for (const x of arr) {
    if (x > 0) return x;
  }
  return null;
}

function b(arr) {
  arr.forEach(x => {
    if (x > 0) return x;
  });
  return null;
}

Why does a([1,2,3]) return 1 but b([1,2,3]) returns null?

A Because return inside forEach only exits the callback, not the outer function

B Because for-of loops do not support return statements

C Because forEach automatically returns the first truthy value

D Because return inside forEach throws an error

💡 Hint

Think about what return does inside a callback function vs a loop.

Return inside a for-of loop exits the whole function immediately. Return inside a forEach callback only exits that callback, not the outer function.