JavaScript

This page explains how filter() creates a new array containing only the elements that satisfy a condition.

Goal: keep the elements whose callback returns true, without changing the original array.

filter()

Use filter() when you want all matching elements, such as all even numbers or all users above a certain age. The callback runs once for each element.

A small example

const numbers = [1, 2, 3, 4, 5, 6];
const evenNumbers = numbers.filter(number => number % 2 === 0);

console.log(evenNumbers); // [2, 4, 6]
console.log(numbers);     // [1, 2, 3, 4, 5, 6]

The expression number % 2 === 0 returns true for even numbers, so only those numbers are copied into the new array.

Filtering objects

const users = [
  { name: "Aki", age: 17 },
  { name: "Ren", age: 22 }
];

const adults = users.filter(user => user.age >= 18);
// [{ name: "Ren", age: 22 }]

Common uses and cautions

• Extract records that match a search or status.
• Remove empty strings or unwanted values with an explicit condition.
• filter() returns all matches, not just the first one.
• Use find() when you need the first matching element.
• The original array is not changed, but the objects inside it are not deeply cloned.

Related topics