JavaScript Array includes() Method

Summary: In this tutorial, you will learn how to use the JavaScript Array includes() method to check if an array includes an element.

Introduction to the JavaScript Array includes() method #

The Array includes() method returns true if an array contains an element or false otherwise.

Here’s the syntax of the includes() method:

array.includes(searchElement, fromIndex)

The includes() method accepts two arguments:

searchElement is the array element you want to search.
fromIndex is a zero-based index at which the method starts searching for searchElement. The default is zero.

The fromIndex can be positive or negative.

If fromIndex >= array.length, then the includes() will not search for the searchElement and returns false.

When 0 <= fromIndex < array.length , then the includes() searches from the fromIndex to the end of the array.

In case -array.length <= fromIndex < 0, fromIndex + array.length , the includes() method searches entires array for searchElement.

JavaScript Array includes() method examples #

Let’s take some examples of using the Array includes() method.

1) Basic Array includes() method examples #

The following example uses the includes() method to check if a number is included in an array:

const numbers = [1, 2, 3];
const result = numbers.includes(1);

console.log({ result });

Output:

{ result: true }

How it works.

First, define an array of numbers:

const numbers = [1, 2, 3];

Second, check if the number 1 is included in the array using the includes() method:

const result = numbers.includes(1);

Third, display the result in the console:

console.log({ result });

Since the number 1 is included in the array, the includes() method returns true.

The following example uses the includes() method to check if the number 3 is included in the numbers array:

const numbers = [1, 2, 3];
const result = numbers.includes(4);

console.log({ result });

Output:

{ result: false }

The includes() method returns false because the numbers array does not contain the number 4.

2) Using the fromIndex argument #

The following example uses the includes() method with the fromIndex to check if an array contains the number 1 from the index 1:

const numbers = [1, 2, 3];
const result = numbers.includes(1, 1);

console.log({ result });

Output:

{ result: false }

The includes() returns false because there is no number 1 starting from the index 1.

3) Using Array includes() method with arrays of objects #

The following example uses the includes() method to check if an object is in an array.

const bmw = { name: 'BMW' };
const toyota = { name: 'Toyota' };
const ford = { name: 'Ford' };

const cars = [ford, toyota];

console.log(cars.includes(ford)); 
console.log(cars.includes(bmw));

How it works.

First, create some objects that have the name property with different values:

const bmw = { name: 'BMW' };
const toyota = { name: 'Toyota' };
const ford = { name: 'Ford' };

Second, initialize the cars array with two objects ford and toyota:

const cars = [ford, toyota];

Third, check if the cars array contains the ford object using the includes() method and display the result to the console:

console.log(cars.includes(ford));

It returns true because the cars object contains the ford object.

Finally, check ifbmw object is included in the cars array:

console.log(cars.includes(bmw));

It returns false.

includes vs. indexOf #

In JavaScript, NaN is not equal to NaN, so both expressions below return false:

let result =  NaN == NaN;
console.log({result});

result =  NaN === NaN;
console.log({result});

The indexOf() method returns -1 when you check if an array contains NaN, but the include() method returns true. For example:

const arr = [1, NaN, 2, 3];

let result = arr.indexOf(NaN);
console.log({ result }); // -1

result = arr.includes(NaN);
console.log({ result }); // true

Output:

{ result: -1 }
{ result: true }

Summary #

Use the JavaScript Array includes() method to check if an element is included in an array.

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