This content originally appeared on DEV Community and was authored by Muhammad Hamza
If I had a dollar for every time I saw someone use .map() just to iterate over an array... I'd have enough to buy multiple MacBook Pro 💰😂.
We all love clean, readable code, but did you know choosing the wrong loop can silently kill your app’s performance? Let's break it down:
🚀 .map() – Elegant, but at What Cost?
const numbers = [1, 2, 3, 4, 5];
const doubled = numbers.map(num => num * 2);
✅ Returns a new array (functional, pure)
❌ Bad if you’re just looping without storing the result
🔥 .forEach() – Looks Simple, but Beware!
numbers.forEach(num => console.log(num * 2));
✅ Great for side effects (logging, updating state)
❌ Cannot be stopped (No break or return)
🏎️ for Loop – Old-School, but Blazing Fast
for (let i = 0; i < numbers.length; i++) {
console.log(numbers[i] * 2);
}
✅ Fastest (optimized at a lower level)
✅ More control (break, continue)
❌ Less readable than .map()
When to Use What?
✅ Use .map() when you need a new transformed array
✅ Use .forEach() when performing side effects
✅ Use for loops when performance is critical
🚀 Pro Tip: If you're iterating over millions of elements, use for loops or even for-of for speed. I’ve seen teams cut processing time by 30%+ just by switching away from .forEach() in performance-critical areas.
💡 What’s your go-to looping method? Drop your thoughts below!
This content originally appeared on DEV Community and was authored by Muhammad Hamza
Muhammad Hamza | Sciencx (2025-02-24T17:35:25+00:00) The Silent Performance Killer in JavaScript: map() vs. forEach() vs. for Loops. Retrieved from https://www.scien.cx/2025/02/24/the-silent-performance-killer-in-javascript-map-vs-foreach-vs-for-loops/
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