Loop Types and Use Cases
for loop works well when iteration count is known.
while loop suits condition-driven repetition with unknown iteration count.
for...of is ideal for clean iteration over arrays and iterables.
JavaScript Tutorial
JavaScript Loops: for, while, for...of, and Control Flow
Loops execute repeated logic efficiently. Choosing the right loop type improves clarity and performance.
Why this matters
Iteration appears in almost all programs for data processing, validation, rendering, and analytics.
Loop Control Statements
Use break to stop a loop early when target condition is met.
Use continue to skip only current iteration and proceed with next.
Avoid infinite loops by ensuring condition updates happen correctly.
Code Examples
const nums = [10, 20, 30, 40];
let total = 0;
for (let i = 0; i < nums.length; i++) {
total += nums[i];
}
console.log(total);Classic loop for indexed data and aggregation.
const users = ["Asha", "", "Ravi", "Nina"];
for (const name of users) {
if (!name) continue;
console.log("User:", name);
}for...of improves readability over manual indexing when index is not needed.
let attempts = 0;
let success = false;
while (attempts < 3 && !success) {
attempts += 1;
success = attempts === 3;
}
console.log("Attempts:", attempts, "Success:", success);while is useful for retry logic and conditional polling patterns.
Common Mistakes and Fixes
Forgetting loop condition updates
Always verify counter increments/decrements to avoid infinite loops.
Using for...in with arrays
Use for...of for array values. for...in is for object keys.
Heavy logic inside loops
Extract complex logic into helper functions for readability and testing.
Frequently Asked Questions
Which loop is best in JavaScript?
Depends on use case. for...of is readable for values, for is useful for indexed control.
Is while loop slower than for loop?
Differences are usually small. Prioritize clarity and correctness first.
Can I break from forEach?
No. Use for, for...of, or array methods like some/find for early-exit behavior.
How do I avoid infinite loops?
Ensure loop condition can become false and update loop variables correctly.