Definition and Usage

The includes() function for arrays checks whether a given array contains a specified element and returns true if it does, or false otherwise.

Using this function is very useful for checking whether a given array contains a specified element.

If the element being searched for is a string, the comparison is case-sensitive.

Basic Example

JavaScript 
const arr = [1, 2, 3, 4, 5];

console.log(arr.includes(3)); // Output: true
console.log(arr.includes(6)); // Output: false

In strings, the includes() function checks whether a specific substring is present in a string.

Syntax

JavaScript 
arr.includes(searchElement)
arr.includes(searchElement, fromIndex)

arr is the array to which the includes() function is applied.

Parameters

Parameters of the Array includes() Function
searchElement The element to search for in the array.
fromIndex Optional. A 0-based index indicating the position at which to begin the search.
If omitted, the default value 0 is used. (Array indexes start at 0.)
If a negative value is provided, the search starts at array.length + fromIndex.

Return Value

The function returns true if the given array contains the specified element. If it does not contain the specified element, it returns false.

Parameter and Return Value Examples

Distinguishing Data Types

In arrays, the includes() function clearly distinguishes the data type of the element being searched for.

JavaScript 
const numbers = [10, 20, 30, 40, NaN];
console.log(numbers.includes(30)); // true
console.log(numbers.includes("30")); // false
console.log(numbers.includes(15)); // false
console.log(numbers.includes(40, 3)); // true
console.log(numbers.includes(20, -2)); // false
console.log(numbers.includes(NaN, -2)); // true

const words = ["apple", "banana", "orange", "grape", "1"];

console.log(words.includes("banana")); // true
console.log(words.includes("pear")); // false
console.log(words.includes("grape", 2)); // true
console.log(words.includes("apple", -4)); // false
console.log(words.includes("banana", -4)); // true
console.log(words.includes(1)); // false
Case Sensitivity of Strings

In arrays, the includes() function performs a case-sensitive comparison when the searched element is a string.

JavaScript 
const words = ["apple", "banana", "orange"];

console.log(words.includes("apple")); // true
console.log(words.includes("Apple")); // false
Exact String Matching

When the searched element is a string, the includes() function returns true only if the given string exactly matches an element in the array. If only part of the string matches, it returns false.

JavaScript 
const words = ["apple", "banana", "orange"];

console.log(words.includes("banana")); // true
console.log(words.includes("ban")); // false
Checking for the Presence of a Variable
JavaScript 
const car = "My car";
const words = ["apple", "banana", car];

console.log(words.includes(car)); // true
console.log(words.includes("My car")); // true

Things to Keep in Mind

There are several important points to be aware of when using the includes() function.

Comparing and Including NaN

In JavaScript, NaN is not equal to itself. That is, NaN === NaN always evaluates to false.
However, when working with arrays, you can use the includes() function to check whether an array contains NaN.

JavaScript 
console.log(NaN === NaN); // false

const values = [1, NaN, 3, 4, 5];
console.log(values.includes(NaN)); // true

Using includes() with Sparse Arrays

When searching for undefined in a sparse array, the includes() function returns true.

JavaScript 
const arr = [1, , 3];
console.log(arr.includes(undefined)); // true

Compatibility

Compatibility for JavaScript Array includes() Function
Method
Desktop Chrome
Chrome
DesktopDesktop Edge
Edge
Desktop Firefox
Firefox
Safari
Safari
Node.js
Node.js
includes() 47 14 43 9 6

Specifications

Specification for JavaScript Array includes() Function
Specification
includes() ECMAScript® 2026 Language Specification
#sec-array.prototype.includes

References

See also