While loop in Javascript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print numbers from 1 to 5 using a while loop.

Javascript

let i = 1;
while (i [1] 5) {
  console.log(i);
  i++;
}

Drag options to blanks, or click blank then click option'

A>

B<

C>=

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'i < 5' which stops at 4.

Using 'i > 5' which never runs the loop.

The condition i <= 5 ensures the loop runs while i is 1 through 5.

2fill in blank

medium

Complete the code to stop the loop when the variable 'count' reaches 10.

Javascript

let count = 0;
while (count [1] 10) {
  console.log(count);
  count++;
}

Drag options to blanks, or click blank then click option'

A<

B>

C<=

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'count <= 10' which runs one extra time.

Using 'count > 10' which never runs the loop.

Using 'count < 10' stops the loop before count reaches 10, so it prints 0 to 9.

3fill in blank

hard

Fix the error in the loop condition to avoid an infinite loop.

Javascript

let n = 5;
while (n [1] 0) {
  console.log(n);
  n--;
}

Drag options to blanks, or click blank then click option'

A<=

B>

C>=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'n >= 0' which runs one extra time including 0.

Using 'n < 0' which never runs the loop.

Using 'n > 0' ensures the loop stops when n reaches 0, preventing an infinite loop.

4fill in blank

hard

Fill both blanks to create a loop that prints even numbers from 2 to 10.

Javascript

let num = [1];
while (num [2] 10) {
  console.log(num);
  num += 2;
}

Drag options to blanks, or click blank then click option'

A2

B<=

C<

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Starting at 0 which prints 0 as well.

Using '<' which stops before printing 10.

Start at 2 and loop while num is less than or equal to 10 to print even numbers up to 10.

5fill in blank

hard

Fill all three blanks to create a loop that counts down from 9 to 1.

Javascript

let i = [1];
while (i [2] [3]) {
  console.log(i);
  i--;
}

Drag options to blanks, or click blank then click option'

A9

B>

C0

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' which would never run the loop.

Using 1 instead of 0 which stops too early.

Start at 9 and loop while i is greater than 0 to count down to 1.

Practice

1. What does a while loop do in JavaScript?

easy

A. Repeats code while a condition is true

B. Runs code only once

C. Runs code a fixed number of times

D. Stops the program immediately

Solution

1. Step 1: Understand the purpose of a while loop

   A while loop runs repeatedly as long as its condition stays true.

2. Step 2: Compare options with the definition

   Only Repeats code while a condition is true correctly describes this behavior.

3. Final Answer:

   Repeats code while a condition is true -> Option A

4. Quick Check:

   while loop = repeats while true [OK]

Hint: Remember: while loops run only if condition is true [OK]

Common Mistakes:

• Thinking while loops run a fixed number of times
• Confusing while with if statement
• Assuming while loops run at least once

2. Which of the following is the correct syntax for a while loop in JavaScript?

easy

A. while condition { /* code */ }

B. while (condition) { /* code */ }

C. while: (condition) { /* code */ }

D. while (condition); { /* code */ }

Solution

1. Step 1: Recall JavaScript while loop syntax

   The correct syntax uses parentheses around the condition and curly braces for the code block: while (condition) { ... }.

2. Step 2: Check each option

   while (condition) { /* code */ } matches the correct syntax exactly.

3. Final Answer:

   while (condition) { /* code */ } -> Option B

4. Quick Check:

   Correct syntax = while (condition) { } [OK]

Hint: Look for parentheses around condition and braces for code [OK]

Common Mistakes:

• Omitting parentheses around the condition
• Using a semicolon after while condition
• Adding a colon after while keyword

3. What will be the output of this code?

let count = 1;
while (count <= 3) {
  console.log(count);
  count++;
}

medium

A. 0 1 2 3

B. 1 2 3 4

C. 3 2 1

D. 1 2 3

Solution

1. Step 1: Analyze the loop condition and increments

   The loop starts with count = 1 and runs while count is less than or equal to 3. Each time, it prints count and then adds 1.

2. Step 2: Trace the output values

   It prints 1, then 2, then 3. When count becomes 4, the condition fails and loop stops.

3. Final Answer:

   1 2 3 -> Option D

4. Quick Check:

   Prints 1 to 3 inclusive [OK]

Hint: Count starts at 1 and stops after 3 [OK]

Common Mistakes:

• Including 4 in output
• Starting count at 0 instead of 1
• Printing in reverse order

4. Find the error in this code snippet:

let i = 0;
while i < 5 {
  console.log(i);
  i++;
}

medium

A. Missing semicolon after console.log

B. Variable i is not declared

C. Missing parentheses around the condition

D. Increment operator is incorrect

Solution

1. Step 1: Check while loop syntax

   JavaScript requires parentheses around the condition in a while loop.

2. Step 2: Identify the error in the code

   The code has while i < 5 { but it should be while (i < 5) {.

3. Final Answer:

   Missing parentheses around the condition -> Option C

4. Quick Check:

   while needs (condition) [OK]

Hint: Always put condition inside parentheses in while [OK]

Common Mistakes:

• Forgetting parentheses around condition
• Adding semicolon after while condition
• Misusing increment operator

5. You want to print all even numbers from 2 to 10 using a while loop. Which code correctly does this?

hard

A. let num = 2;
while (num <= 10) {
console.log(num);
num += 2;
}

B. let num = 1;
while (num < 10) {
if (num % 2 === 0) console.log(num);
num++;
}

C. let num = 2;
while (num < 10) {
console.log(num);
num += 2;
}

D. let num = 0;
while (num <= 10) {
console.log(num);
num += 2;
}

Solution

1. Step 1: Understand the goal and loop conditions

   We want to print even numbers from 2 to 10 inclusive. So the loop must start at 2 and run while number is less than or equal to 10.

2. Step 2: Check each option for correctness

   let num = 2; while (num <= 10) { console.log(num); num += 2; } starts at 2, prints number, then adds 2, stopping at 10. This prints 2,4,6,8,10 correctly. let num = 1; while (num < 10) { if (num % 2 === 0) console.log(num); num++; } starts at 1, uses modulo check, but since num < 10 stops after 9, printing 2,4,6,8 missing 10. let num = 2; while (num < 10) { console.log(num); num += 2; } stops before 10, missing 10. let num = 0; while (num <= 10) { console.log(num); num += 2; } starts at 0, which is not in the required range.

3. Final Answer:

   let num = 2; while (num <= 10) { console.log(num); num += 2; } -> Option A

4. Quick Check:

   Start 2, add 2, stop at 10 [OK]

Hint: Start at 2, add 2 each loop, stop at 10 [OK]

Common Mistakes:

• Starting at 0 or 1 instead of 2
• Stopping before 10
• Not incrementing by 2