Do–while loop in Javascript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple do–while loop

What is the output of this JavaScript code?

Javascript

let count = 0;
do {
  console.log(count);
  count++;
} while (count < 3);

A 1 2 3

B 0 1 2

C 0 1 2 3

D 1 2

💡 Hint

Remember, do–while runs the block first, then checks the condition.

The loop starts with count = 0, prints it, then increments. It repeats while count < 3, so it prints 0, 1, and 2.

❓ Predict Output

intermediate

Do–while loop with break statement

What will this code print to the console?

Javascript

let i = 5;
do {
  console.log(i);
  if (i === 3) break;
  i--;
} while (i > 0);

A 5 4 3

B 5 4 3 2 1

C 5 4

D 3 2 1

💡 Hint

The break stops the loop when i equals 3.

The loop prints 5, then 4, then 3. When i is 3, break stops the loop immediately.

🧠 Conceptual

advanced

Understanding do–while loop execution

Which statement about do–while loops is true?

A Do–while loops cannot be used to run code multiple times.

B The loop body may not execute if the condition is false at the start.

C The condition is checked before the loop body runs.

D The loop body executes at least once, even if the condition is false initially.

💡 Hint

Think about when the condition is checked in a do–while loop.

In a do–while loop, the code inside the loop runs first, then the condition is checked. So it always runs at least once.

❓ Predict Output

advanced

Output with nested do–while loops

What is the output of this nested do–while loop code?

Javascript

let a = 1;
do {
  let b = 1;
  do {
    console.log(a * b);
    b++;
  } while (b <= 2);
  a++;
} while (a <= 2);

A 1 2 2 4

B 1 2 1 2

C 2 4 2 4

D 1 2 3 4

💡 Hint

Trace the values of a and b carefully through both loops.

Outer loop runs for a=1 and a=2. Inner loop runs for b=1 and b=2 each time. Outputs: 1*1=1, 1*2=2, 2*1=2, 2*2=4.

🔧 Debug

expert

Identify the error in this do–while loop

What error will this code cause when run?

Javascript

let x = 0;
do {
  console.log(x);
  x++
} while x < 3;

A ReferenceError

B TypeError

C SyntaxError

D No error, outputs 0 1 2

💡 Hint

Check the syntax of the while condition in a do–while loop.

The while condition must be inside parentheses. Missing parentheses causes SyntaxError.