The Silent Performance Killer in JavaScript: map() vs. forEach() vs. for Loops

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()

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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

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🚀 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!

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