For loop in Javascript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple for loop

What will be the output of the following code?

Javascript

let result = '';
for (let i = 0; i < 3; i++) {
  result += i + '-';
}
console.log(result);

A "0-1-2-"

B "0-1-2"

C "1-2-3-"

D "0-1-2-3-"

💡 Hint

Remember the loop runs while i is less than 3, starting from 0.

The loop runs with i values 0, 1, and 2. Each time it adds i and a dash to the string. So the final string is "0-1-2-".

❓ Predict Output

intermediate

For loop with break statement

What will be printed by this code?

Javascript

let sum = 0;
for (let i = 1; i <= 5; i++) {
  if (i === 3) break;
  sum += i;
}
console.log(sum);

A 0

B 6

C 10

D 3

💡 Hint

The loop stops when i equals 3.

The loop adds 1 and 2 to sum, then stops before adding 3. So sum is 1 + 2 = 3.

❓ Predict Output

advanced

Nested for loops output

What is the output of this nested loop code?

Javascript

let output = '';
for (let i = 1; i <= 2; i++) {
  for (let j = 1; j <= 3; j++) {
    output += `${i}${j} `;
  }
}
console.log(output.trim());

A "11 12 13 21 22 23"

B "11 21 12 22 13 23"

C "123 123"

D "1 2 3 1 2 3"

💡 Hint

The outer loop runs twice, inner loop runs three times each.

For i=1, j runs 1 to 3 producing 11 12 13. For i=2, j runs 1 to 3 producing 21 22 23. Combined output is "11 12 13 21 22 23".

❓ Predict Output

advanced

For loop with continue statement

What will this code print?

Javascript

let text = '';
for (let i = 0; i <= 5; i++) {
  if (i % 2 === 0) continue;
  text += i;
}
console.log(text);

A "024"

B "1234"

C "135"

D "0246"

💡 Hint

Continue skips even numbers.

The loop skips i when it is even (0,2,4). It adds only odd numbers 1, 3, and 5 to text, so output is "135".

❓ Predict Output

expert

For loop with asynchronous behavior

What will be logged to the console when this code runs?

Javascript

for (let i = 0; i < 3; i++) {
  setTimeout(() => console.log(i), 0);
}

A 3 3 3

B 0 1 2

C 0 0 0

D 1 2 3

💡 Hint

The variable i is declared with let inside the loop.

Using let creates a new binding for each loop iteration, so the logged values are 0, 1, and 2 as expected.