How To Use the filter() Array Method in JavaScript

Introduction

The filter() Array method creates a new array with elements that fall under a given criteria from an existing array.

In this article, you will learn about the filter() Array method.

Prerequisites

If you would like to follow along with this article, you will need:

• Some familiarity with JavaScript Arrays.
• Some familiarity with JavaScript Functions.

Using filter() on an Array of Numbers

The syntax for filter() resembles:

var newArray = array.filter(function(item) {
  return condition;
});

The item argument is a reference to the current element in the array as filter() checks it against the condition. This is useful for accessing properties, in the case of objects.

If the current item passes the condition, it gets returned to the new array.

Consider this example array of numbers:

var numbers = [1, 3, 6, 8, 11];

Then apply a filter() to return all numbers that are greater than 7:

var greaterThanSeven = numbers.filter(function(number) {
  return number > 7;
});

console.log(greaterThanSeven);

This code will generate a new filtered array:

output
[8, 11]

An array with two values greater than 7 is returned.

Using filter() on an Array of Objects

A common use case of filter() is with an array of objects through their properties.

Consider this example array of creature objects:

var creatures = [
  {name: "Shark", habitat: "Ocean"},
  {name: "Whale", habitat: "Ocean"},
  {name: "Lion", habitat: "Savanna"},
  {name: "Monkey", habitat: "Jungle"}
];

Then apply a filter() to return all creatures with a habitat that is equal to Ocean:

var aquaticCreatures =  creatures.filter(function(creature) {
  return creature.habitat == "Ocean";
});

console.log(aquaticCreatures);

This code will generate a new filtered array:

Output
[ {name: "Shark", habitat: "Ocean"}, {name: "Whale", habitat: "Ocean"} ]

An array with the two creatures that have a habitat in the “Ocean” is returned.

Conclusion

In this article, you learned about the filter() Array method.

For more details, consult the MDN Reference on filter().

Filter is only one of several iteration methods on Arrays in JavaScript, read How To Use Array Iteration Methods in JavaScript to learn about the other methods like map() and reduce().