Differences between JavaScript map, filter, reduce, and for...of

• map: creates a new array by transforming each element.
• filter: creates a new array with only elements that pass a condition.
• reduce: reduces all elements into a single value.
• for...of: a simple loop to go through each element without creating a new array.

const nums = [1, 2, 3, 4, 5];

// map → multiply by 2
const doubled = nums.map(n => n * 2);
// [2, 4, 6, 8, 10]

// filter → keep evens
const evens = nums.filter(n => n % 2 === 0);
// [2, 4]

// reduce → sum
const sum = nums.reduce((acc, n) => acc + n, 0);
// 15

// for...of → plain iteration
for (const n of nums) {
  console.log(n); // 1, 2, 3, 4, 5
}

Method	Return Value	Performance	Best Use Case	Creates New Array?
map	Array (same length)	Medium	Transform all elements	✅ Yes
filter	Array (≤ length)	Medium	Select elements matching a condition	✅ Yes
reduce	Single value	Medium-Slower	Aggregate/combine into one result	❌ No
for...of	None (just loop)	Fastest	Plain iteration, side-effects, max performance	❌ No