1. What is the main purpose of a while loop in JavaScript?
a) To iterate over the properties of an object
b) To execute a block of code as long as a specified condition is true
c) To execute a block of code a fixed number of times
d) To handle exceptions
Answer:
b) To execute a block of code as long as a specified condition is true
Explanation:
A while loop in JavaScript is used to execute a block of code repeatedly as long as a specified condition remains true.
2. What is the basic syntax of a while loop in JavaScript?
a) while (condition) {…}
b) while condition {…}
c) while {condition} {…}
d) while [condition] {…}
Answer:
a) while (condition) {…}
Explanation:
The basic syntax of a while loop includes the while keyword followed by a condition in parentheses and a block of code in curly braces.
3. How does a while loop start its execution?
a) By initializing a counter
b) By executing the block of code once
c) By evaluating the condition
d) By incrementing the counter
Answer:
c) By evaluating the condition
Explanation:
A while loop starts its execution by first evaluating the condition. If the condition is true, the loop executes the block of code.
4. What happens if the condition in a while loop never becomes false?
a) The loop stops after a certain number of iterations
b) The loop will execute indefinitely, creating an infinite loop
c) An error is thrown
d) The loop skips the remaining iterations
Answer:
b) The loop will execute indefinitely, creating an infinite loop
Explanation:
If the condition in a while loop never becomes false, the loop will continue to execute indefinitely, resulting in an infinite loop.
5. Can you declare and initialize variables within the while loop condition?
a) Yes
b) No
c) Only if the variable is global
d) Only if the variable is a constant
Answer:
a) Yes
Explanation:
It is possible to declare and initialize variables within the while loop condition, although it is more common to do so before the loop starts.
6. What is the main difference between a while loop and a do-while loop?
a) A do-while loop checks the condition at the end of each iteration
b) A do-while loop is faster than a while loop
c) A while loop can handle multiple conditions
d) A do-while loop cannot use a counter
Answer:
a) A do-while loop checks the condition at the end of each iteration
Explanation:
The main difference is that a do-while loop executes the block of code once before checking the condition, ensuring that the code block is executed at least once.
7. How can you stop the execution of a while loop?
a) Using the stop keyword
b) By setting the condition to false
c) Using the break keyword
d) By omitting the condition
Answer:
c) Using the break keyword
Explanation:
The break keyword can be used within the loop body to exit the loop prematurely and stop its execution.
8. What happens when a break statement is executed inside a while loop?
a) The current iteration is skipped
b) The loop restarts from the beginning
c) The loop execution is terminated immediately
d) The loop continues with the next iteration
Answer:
c) The loop execution is terminated immediately
Explanation:
When a break statement is executed inside a while loop, it terminates the loop's execution immediately and exits the loop.
9. Can a while loop contain another while loop inside it?
a) Yes, this is called a nested loop
b) No, nested loops are not allowed in JavaScript
c) Only if the outer loop is a do-while loop
d) Only if the inner loop has a different condition
Answer:
a) Yes, this is called a nested loop
Explanation:
A while loop can contain another while loop inside it, forming a nested loop structure.
10. Is it necessary for a while loop to have a body with statements?
a) Yes, at least one statement is required
b) No, an empty while loop is allowed
c) Only if the loop has a condition
d) Only if the loop uses a counter
Answer:
b) No, an empty while loop is allowed
Explanation:
A while loop can have an empty body, though it is not common and usually not very useful.
11. How do you ensure that a while loop eventually terminates?
a) By including a break statement
b) By changing the condition to false within the loop
c) By using a counter that changes each iteration
d) Both b and c
Answer:
d) Both b and c
Explanation:
To ensure that a while loop terminates, the condition must eventually evaluate to false. This can be achieved by modifying the condition within the loop or using a counter that changes each iteration.
12. In a while loop, when is the condition re-evaluated?
a) After each iteration of the loop
b) Before the loop starts
c) Only when a break statement is executed
d) When a continue statement is executed
Answer:
a) After each iteration of the loop
Explanation:
In a while loop, the condition is re-evaluated after each iteration to determine if the loop should continue or terminate.
13. Can variables used in a while loop condition be modified inside the loop?
a) Yes
b) No
c) Only global variables
d) Only if they are declared inside the loop
Answer:
a) Yes
Explanation:
Variables used in the condition of a while loop can be modified inside the loop, which is often necessary for the loop to eventually terminate.
14. What is the function of the continue statement in a while loop?
a) To pause the loop
b) To terminate the loop
c) To skip the current iteration and proceed to the next iteration
d) To reset the loop condition
Answer:
c) To skip the current iteration and proceed to the next iteration
Explanation:
The continue statement in a while loop is used to skip the rest of the current iteration and proceed directly to the next iteration.
15. Is it possible for a while loop to execute zero times?
a) Yes, if the condition is false from the start
b) No, it always executes at least once
c) Only if there is a break statement in the first line
d) Only in a nested loop
Answer:
a) Yes, if the condition is false from the start
Explanation:
A while loop will execute zero times if its condition is false from the very beginning, as the condition is checked before the first iteration.