Array.prototype.filter()

filter(callbackFn, thisArg)

Returns: Array · Updated March 13, 2026 · Array Methods

array filter functional

The filter method creates a shallow copy of a portion of a given array, filtered down to just the elements from the given array that pass the test implemented by the provided function.

Syntax

filter(callbackFn)
filter(callbackFn, thisArg)

Parameters

Parameter	Type	Default	Description
callbackFn	function	required	Function to test each element. Return true to keep the element, false otherwise.
element	any	-	The current element being processed.
index	number	-	The index of the current element.
array	Array	-	The array filter was called upon.
thisArg	any	undefined	Value to use as this when executing callbackFn.

Examples

Basic usage

const words = ['spray', 'limit', 'elite', 'exuberant', 'destruction', 'present'];

const result = words.filter(word => word.length > 6);

console.log(result);
// ['exuberant', 'destruction', 'present']

Filtering with index

const numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

// Keep only numbers at even indices
const result = numbers.filter((num, index) => index % 2 === 0);

console.log(result);
// [1, 3, 5, 7, 9]

Filtering objects

const users = [
  { name: 'Alice', age: 25, active: true },
  { name: 'Bob', age: 30, active: false },
  { name: 'Charlie', age: 28, active: true },
  { name: 'Diana', age: 22, active: false }
];

const activeUsers = users.filter(user => user.active);

console.log(activeUsers);
// [{ name: 'Alice', age: 25, active: true },
//  { name: 'Charlie', age: 28, active: true }]

Using thisArg

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

const multiplier = {
  threshold: 3
};

const result = nums.filter(function(num) {
  return num > this.threshold;
}, multiplier);

console.log(result);
// [4, 5]

Common Patterns

Finding unique values

const items = ['apple', 'banana', 'apple', 'orange', 'banana', 'apple'];

const unique = items.filter((item, index) => items.indexOf(item) === index);

console.log(unique);
// ['apple', 'banana', 'orange']

Filtering by multiple criteria

const products = [
  { name: 'Laptop', price: 999, inStock: true },
  { name: 'Mouse', price: 29, inStock: true },
  { name: 'Keyboard', price: 79, inStock: false },
  { name: 'Monitor', price: 299, inStock: true }
];

const affordableInStock = products.filter(p => p.inStock && p.price < 100);

console.log(affordableInStock);
// [{ name: 'Mouse', price: 29, inStock: true }]

Removing falsy values

const mixed = [0, 1, 'hello', '', null, undefined, true, false, 42];

const truthy = mixed.filter(Boolean);

console.log(truthy);
// [1, 'hello', true, 42]