These are the methods that come up in real work. Terse by design — this is a reference, not a tutorial.
const nums = [1, 2, 3, 4, 5];
// Transform every element — returns a new array
nums.map(n => n * 2); // [2, 4, 6, 8, 10]
// Keep elements matching a predicate
nums.filter(n => n % 2 === 0); // [2, 4]
// Accumulate to a single value
nums.reduce((acc, n) => acc + n, 0); // 15
// First match — returns the element or undefined
nums.find(n => n > 3); // 4
// Does every / any element satisfy the predicate?
nums.every(n => n > 0); // true
nums.some(n => n > 4); // true
// Flatten one level deep — useful after a map that returns arrays
[[1, 2], [3, 4]].flat(); // [1, 2, 3, 4]
nums.flatMap(n => [n, n * 2]); // [1,2, 2,4, 3,6, 4,8, 5,10]None of these mutate the original array. reduce is the most general-purpose — map and filter are both expressible as reduces, but prefer the specific methods when the intent is clear.