JavaScript Loops: When and How to Use Them

Loops are fundamental in JavaScript—they help you execute a block of code repeatedly. But with different types of loops available, it's important to know when and how to use each one effectively.

1. for Loop

When to use:

• When you know exactly how many times you need to iterate.
• Ideal for arrays when you need the index.

Example:

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

2. while Loop

When to use:

• When the number of iterations is unknown and depends on a condition.
• Useful for reading streams or waiting for a condition to be met.

Example:

let count = 0;
while (count < 5) {
  console.log(count); // 0, 1, 2, 3, 4
  count++;
}

3. do...while Loop

When to use:

• When you want the loop to run at least once, even if the condition is false.

Example:

let x = 0;
do {
  console.log(x); // 0 (runs once even if condition is false)
  x++;
} while (x < 0);

4. for...of Loop

When to use:

• When iterating over arrays, strings, or other iterable objects.
• Cleaner syntax when you don’t need the index.

Example:

const arr = [1, 2, 3];
for (const num of arr) {
  console.log(num); // 1, 2, 3
}

5. for...in Loop

When to use:

• When iterating over object properties (keys).
• Avoid using for arrays (use for...of instead).

Example:

const obj = { a: 1, b: 2 };
for (const key in obj) {
  console.log(key, obj[key]); // "a 1", "b 2"
}

6. Array.forEach()

When to use:

• When you want to execute a function on each array element.
• Doesn’t return a new array (unlike map()).

Example:

const numbers = [1, 2, 3];
numbers.forEach(num => console.log(num * 2)); // 2, 4, 6

Key Takeaways

✅ Use for when you know the iteration count.

✅ Use while/do...while for condition-based looping.

✅ Use for...of for arrays and iterables.

✅ Use for...in for object properties (but check hasOwnProperty).

✅ Use forEach for simple array iteration (but note it doesn’t break early).

Which loop do you use most often? Let me know in the comments! 🚀