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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