JavaScript Loops — Interview Questions & Answers

Ques: What are loops in JavaScript?

Ans: Loops are used to execute a block of code repeatedly until a certain condition is met. They help reduce repetition and make the code cleaner.

Common loop types in JavaScript are:

• for
• while
• do...while
• for...in
• for...of

Ques: What is the syntax of a for loop?

Ans: The for loop runs a block of code a specific number of times.

Syntax:

for (initialization; condition; increment) {
  // code to execute
}

Example:

for (let i = 1; i <= 5; i++) {
  console.log(i);
}

Output:

1
2
3
4
5

Ques: How does a while loop work?

Ans: A while loop runs as long as the condition is true. It checks the condition before each iteration.

Example:

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

Output:

Hello
Hello
Hello

Ques: What is a do...while loop?

Ans: The do...while loop executes at least once, even if the condition is false, because the condition is checked after the first execution.

Example:

let num = 5;
do {
  console.log(num);
  num++;
} while (num < 5);

Output:

5

Ques: What is the difference between while and do...while loops?

Ques: What is the for...in loop used for?

Ans: The for...in loop is used to iterate over object properties (keys).

Example:

const person = { name: "Alice", age: 25 };
for (let key in person) {
  console.log(key + ": " + person[key]);
}

Output:

name: Alice
age: 25

Ques: What is the for...of loop used for?

Ans: The for...of loop is used to iterate over iterable objects like arrays, strings, maps, etc.

Example:

const colors = ["red", "green", "blue"];
for (let color of colors) {
  console.log(color);
}

Output:

red
green
blue

Ques: What is the difference between for...in and for...of?

Ques: What are break and continue statements in loops?

• break → Exits the loop completely.
• continue → Skips the current iteration and moves to the next one.

Example:

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

Output:

1
2
4

Ques : Can loops be nested in JavaScript?

Ans: Yes, You can place a loop inside another loop — called a nested loop.

Example:

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

Output:

i=1, j=1
i=1, j=2
i=1, j=3
i=2, j=1
i=2, j=2
i=2, j=3

Ques : What are infinite loops?

Ans: An infinite loop occurs when the condition never becomes false, causing the loop to run endlessly.

Example:

while (true) {
  console.log("Running forever...");
}