How Do I Check if an Array Includes a Value in JavaScript?

Given an array and a value, the task is to check whether an array includes a value in JavaScript. There are various ways to check an array includes a value in JavaScript.

1. Using includes() Method

The includes() method is the simplest and most readable way to check if an array contains a value. It checks for the existence of a specified value and returns true if found, otherwise false.

const arr = [10, 20, 30, 40, 50];
console.log(arr.includes(20)); // Output: true
console.log(arr.includes(25));  // Output: false

2. Using indexOf() Method

The indexOf() method returns the index of the first occurrence of a specified value in an array. If the value is not found, it returns -1.

const arr = [10, 20, 30, 40, 50];
console.log(arr.indexOf(30) !== -1); // Output: true
console.log(arr.indexOf(70) !== -1); // Output: false

3. Using find() or findIndex() Methods

The find() method returns the first element that satisfies a provided testing function, while findIndex() returns the index of the first matching element. Both can be used to check if a value exists in an array by applying a custom condition.

const arr = [10, 20, 30, 40, 50];
console.log(arr.find(item => item === 70) !== -1);
// Output: true

4: Using a for or forEach Loop

A manual loop allows complete control over the search logic. This is useful for customized searches or for environments that lack modern JavaScript features.

Example with for Loop

const arr = [10, 20, 30, 40, 50];
let found = false;

for (let i = 0; i < arr.length; i++) {
    if (arr[i] === 30) {
        found = true;
        break;
    }
}

console.log(found); // Output: true

Example with forEach()

const arr = [10, 20, 30, 40, 50];
let found = false;

arr.forEach(item => {
    if (item === 30) 
        found = true;
});

console.log(found); // Output: true

5: Using some() Method

The some() method checks if at least one element in an array satisfies a given condition. It returns true if the condition is met for any element, otherwise false.

const arr = [10, 20, 30, 40, 50];

console.log(arr.some(item => item === 30)); // Output: true
console.log(arr.some(item => item === 60)); // Output: false

6: Using Set for Faster Lookups

If you frequently check for values in an array, converting it to a Set can improve performance because Set.has() is faster for lookups compared to array methods.

const arr = [10, 20, 30, 40, 50];
const numbersSet = new Set(arr);

console.log(numbersSet.has(30)); // Output: true
console.log(numbersSet.has(60)); // Output: false