JavaScript Array includes()

// defining an array
let languages = ["JavaScript", "Java", "C"];

// checking whether the array contains 'Java'
let check = languages.includes("Java");

console.log(check); 

// Output: true

includes() Syntax

The syntax of the includes() method is:

arr.includes(valueToFind, fromIndex)

Here, arr is an array.

includes() Parameters

The includes() method can take two parameters:

• searchValue- The value to search for.
• fromIndex (optional) - The position in the array at which to begin the search. By default, it is 0.

Note: For negative values, the search starts from array.length + fromIndex (Counting from backward). For example, -1 represents the last element.

includes() Return Value

The includes() method returns:

• true if searchValue is found anywhere within the array
• false if searchValue is not found anywhere within the array

Example 1: Using includes() method

let languages = ["JavaScript", "Java", "C", "C++"];

// checking whether the array contains 'C'
let check1 = languages.includes("C");

console.log(check1); // true

// checking whether the array contains 'Ruby'
let check2 = languages.includes("Ruby");

console.log(check2); // false

Output

true
false

In the above example, we have used the includes() method to check whether the languages array contains elements 'C' and 'Ruby'.

languages.includes("C") returns true since the array contains 'C' and languages.includes("Ruby") returns false since the array does not contain 'Ruby'.

Example 2: includes() for Case-Sensitive Search

The includes() method is case sensitive. For example:

let languages = ["JavaScript", "Java", "C", "Python"];

// checking whether the array contains 'Python'
let check1 = languages.includes("Python");

console.log(check1); // true

// checking whether the array contains 'python'
let check2 = languages.includes("python");

console.log(check2); // false

Output

true
false

Here the includes() method returns true for searchValue- 'Python' and false for 'python'.

This is because the method is case sensitive and it treats 'Python' and 'python' as two different strings.

Example 3: includes() with two Parameters

let languages = ["JavaScript", "Java", "C", "Python"];

// second argument specifies position to start the search
let check1 = languages.includes("Java", 2);

console.log(check1); // false

// the search starts from third last element 
let check2 = languages.includes("Java", -3);

console.log(check2); // true 

Output

false
true

In the above example, we have passed two argument values in the include() method.

languages.includes("Java", 2) returns false since the method doesn't find 'Java' from second index of the array.

In languages.includes("Java", -3), the method starts searching 'Java' from the third last element because of the negative argument -3.

Recommended Reading: JavaScript Array indexOf()