Loops in JavaScript

What Are Loops?

Loops allow you to repeat a block of code multiple times. Instead of writing the same code 10 times, you write it once and let the loop handle the repetition.

The for Loop

The most common loop. Use it when you know how many times you want to repeat something.

for (let i = 0; i < 5; i++) {
  console.log("Count:", i);
}
// Output: 0, 1, 2, 3, 4

The while Loop

Use when you don't know how many times you'll need to repeat — the loop continues while a condition is true.

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

The do-while Loop

Similar to while, but the code runs at least once before checking the condition.

let x = 5;
do {
  console.log("Do-while:", x);
  x++;
} while (x < 3);
// Runs once even though x is not less than 3

Looping Through Arrays

One of the most common uses of loops is to process each item in an array.

let fruits = ["apple", "banana", "orange"];

for (let i = 0; i < fruits.length; i++) {
  console.log("I like", fruits[i]);
}

Breaking and Continuing

• break — exit the loop immediately
• continue — skip the current iteration and move to the next

for (let i = 0; i < 10; i++) {
  if (i === 5) break;     // stops at 5
  if (i % 2 === 0) continue; // skips even numbers
  console.log(i); // 1, 3
}

Common Mistakes

• Infinite loops — forgetting to increment the counter or update the condition
• Off-by-one errors — using <= instead of < or vice versa
• Modifying the array while iterating over it

Quick Quiz

Summary

• for loops: use when you know the number of iterations
• while loops: use when you don't know the number of iterations
• do-while loops: use when the code must run at least once
• break exits a loop; continue skips to the next iteration
• Always update the loop condition to avoid infinite loops