JavaScript Loops Quiz - Multiple Choice Questions (MCQ)

Loops are fundamental constructs in programming that allow us to execute a block of code repeatedly. In JavaScript, we have various types of loops that serve different purposes. Are you familiar with the concepts of for, while, and do-while loops in JavaScript? 

Let's put your looping knowledge to the test with this JavaScript Loops Quiz! Each question is multiple-choice, and after each question, you'll find the correct answer along with a detailed explanation. Let's dive in and see how well you handle loops in JavaScript!

1. What are the main types of loops available in JavaScript? 

a) for loop, do...while loop, while loop

b) for loop, do...until loop, while loop

c) for loop, while loop, repeat...until loop

d) for loop, do...while loop, repeat...until loop 

Answer: 

a) for loop, do...while loop, while loop

Explanation: 

JavaScript provides three main types of loops - for loop, do...while loop, and while loop. Each loop has its use case and syntax, but they all serve the purpose of repeatedly executing a block of code based on a condition.

2. Which loop is guaranteed to execute the block of code at least once? 

a) for loop 

b) do...while loop 

c) while loop 

d) none

Answer: 

b) do...while loop 

Explanation: 

The do...while loop first executes the block of code and then checks the condition. It will keep executing the code as long as the condition is true. Since the code block is executed before checking the condition, it is guaranteed to run at least once.

3. What does the while loop do?

a) Executes a block of code once and then stops.

b) Executes a block of code repeatedly as long as the condition is true.

c) Executes a block of code repeatedly at a specific interval of time. 

d) Executes a block of code repeatedly until a condition becomes true. 

Answer: 

b) Executes a block of code repeatedly as long as the condition is true. 

Explanation: 

The while loop continues executing the block of code inside it as long as the specified condition is true. If the condition is false from the beginning, the loop won't execute at all.

4. What is the output of the following while loop?

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

a) Hello

b) Hello Hello Hello

c) 0 1 2

d) undefined

Answer:

b) Hello Hello Hello

Explanation:

The while loop will execute as long as the count is less than 3. In each iteration, "Hello" will be logged to the console, and then the count will be incremented by 1. The loop will run three times, and the output will be "Hello Hello Hello".

5. What is the difference between for and while loops?

a) There is no difference; they are interchangeable.

b) for loops are used for a fixed number of iterations, while while loops are used for unknown or dynamically determined iterations. 

c) for loops are used for asynchronous operations, while while loops are used for synchronous operations.

d) for loops are used with arrays, while loops are used with objects. 

Answer: 

b) for loops are used for a fixed number of iterations, while loops are used for unknown or dynamically determined iterations. 

Explanation: 

The for loops are generally used when we know the exact number of iterations in advance, as they provide a clear initialization, condition, and incrementation pattern. On the other hand, while loops are used when the number of iterations depends on a condition that may change during the loop's execution.

6. What does the do-while loop do?

a) Executes a block of code once and then stops. 

b) Executes a block of code repeatedly as long as the condition is true. 

c) Executes a block of code repeatedly at a specific interval of time. 

d) First executes the block of code before checking the condition.

Answer: 

d) First executes the block of code before checking the condition.

Explanation: 

The do-while loop executes the block of code inside it first, and then it checks the condition. If the condition is true, the loop will execute again. It ensures that the block of code is executed at least once, regardless of the condition's initial state.

7. What is the output of the following do-while loop?

let x = 5;
do {
  console.log("Hello");
  x--;
} while (!x > 0);

a) Hello Hello Hello Hello Hello

b) Hello

c) undefined

d) Hello Hello Hello Hello 

Answer: 

b) Hello 

Explanation: 

The do-while loop will execute the block of code once because the condition x > 0 is true initially. After the first iteration, x will be decremented to 4, but the condition becomes false (4 > 0 is true). Therefore, the loop won't execute again, and the output will be "Hello" printed once.

8. What is the correct way to skip the current iteration of a loop in JavaScript?

a) break; 

b) skip; 

c) next; 

d) continue; 

Answer: 

d) continue; 

Explanation: 

The continue statement is used to skip the current iteration of a loop and move on to the next iteration.

9. What is the output of the following loop?

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

a) 0 1 3 4

b) 0 1 2 3 4 

c) 2 4 

d) 0 1 2 4 

Answer: 

a) 0 1 3 4 

Explanation: 

In this for loop, the continue statement is used to skip the iteration when i is equal to 2. So, the loop will not execute the block of code for i equal to 2, resulting in the output 0 1 3 4.

10. What is the key difference between the while loop and the do...while loop? 

a) The while loop executes the code block first, then checks the condition. The do...while loop checks the condition first, then executes the code block.

b) The while loop always executes the code block at least once. The do...while loop checks the condition first and may skip the code block entirely.

c) The while loop is more efficient for larger datasets. The do...while loop is more efficient for smaller datasets.

d) There is no difference between the two; they can be used interchangeably.

Answer: 

a) The while loop executes the code block first, then checks the condition. The do...while loop checks the condition first, then executes the code block. 

Explanation: 

The key difference lies in the order of execution. In a while loop, the condition is evaluated first, and if it's true, the code block is executed. In contrast, the do...while loop executes the code block first and then checks the condition. This ensures that the code block is executed at least once, even if the condition is initially false.

Conclusion

Congratulations on completing the JavaScript Loops Quiz! Loops are powerful tools for automating repetitive tasks in programming, and understanding their behavior is essential for every developer. 

Keep practicing and experimenting with loops to master their usage in different scenarios. Happy coding!