How do I check if an Array includes a value in JavaScript?

In this article, we are going to learn how to check if a value is present in an array or not. To do so we will require the array to search in and the target element whose presence has to be checked. 

JavaScript Arrays are used to store a list of elements that can be accessed by a single variable.

Once we have a target element we can perform any of the search algorithms to check for the presence of the element in the array.

1. Linear Search Algorithm (Naive approach)

In the Linear search algorithm, we compare each element of the array with the target. 8 is part of the num array below.

Javascript

var num = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

function check(element) {

    for (var i = 0; i < num.length; i++) {
        if (num[i] == element)
            return element + " is present in the array.";

    }
    return element + " is not present in the array.";
}
console.log(check(8));

Output

8 is present in the array.

Time complexity: O(n)

The time complexity for this algorithm is O(n) as we are looping through the array once to check for the given element.

Space complexity: O(1)

The space complexity for this algorithm is O(1) as we are not using any additional space other than the input array.

2. Using indexOf() function

The indexOf() function returns the index of the target element in the array if it is present and -1 if not present.

For example, 41 is not part of the num array in the code below.

Javascript

var num = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
var element = 41;
if (num.indexOf(element) > 0)
    console.log(element + " is present.");
else
    console.log(element + " is not present.");

Output

41 is not present.

Time complexity: O(n)
Space complexity: O(1)

3. Binary Search

The Binary search algorithm works only on sorted arrays and keeps dividing the array into 2 equal halves and works recursively.

Javascript

function bsearch(arr, l, r, x) {
    if (r >= l) {
        let mid = l + Math.floor((r - l) / 2);

        if (arr[mid] == x)
            return mid;

        if (arr[mid] > x)
            return bsearch(arr, l, mid - 1, x);

        return bsearch(arr, mid + 1, r, x);
    }

    return -1;

}

var num = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

// To check if 85 is present or not
console.log("Is 85 present? "+(bsearch(num, 0, num.length, 85) != -1));

// To check if 1 is present or not
console.log("Is 1 present? "+(bsearch(num, 0, num.length, 1) != -1));

Output

Is 85 present? false
Is 1 present? true

Time Complexity: O(log n)
Space Complexity: O(1)