What are the most useful array methods you use regularly?

Modern JavaScript array methods make data transformation expressive and readable.

map transforms each element, returning a new array: users.map(u => u.name) extracts names. It's for when you want the same number of items but different values.

filter keeps elements that pass a test: users.filter(u => u.active). Returns a subset of the original array. Often chained with map: filter then transform.

reduce builds a single value from an array: arr.reduce((sum, n) => sum + n, 0) for totals, or building objects, grouping, flattening. It's the most flexible but can be less readable—prefer map/filter when they fit.

find returns the first matching element (or undefined): users.find(u => u.id === id). findIndex returns the index instead. Use these for single-item lookups.

some checks if any element passes a test, every checks if all do. Both return booleans and short-circuit when the answer is determined.

includes checks array membership: [1,2,3].includes(2). Simple but useful for checking existence.

flat and flatMap handle nested arrays. flatMap is especially useful for operations that might return multiple items per input.

These methods return new arrays (except forEach, which is for side effects). Chain them for readable data pipelines: users.filter(...).map(...).sort(...).