JavaScript - Check if JS Array Includes a Value?

Last Updated : 20 Nov, 2024
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To check if an array includes a value we can use JavaScript Array.includes() method. This method returns a boolean value, if the element exists it returns true else it returns false.

1. Using Array.includes() Method - Mostly Used

The JS array.includes() method returns true if the array contains the specified value.

JavaScript 
const a = [10, 20, 30, 40, 50];
let n1 = 30,
	n2 = 45;

const r1 = a.includes(n1);

const r2 = a.includes(n2);

// Display results r1 and r2
console.log(n1, "is Present in Array:", r1);
console.log(n2, "is Present in Array:", r2);

Output
30 is Present in Array: true
45 is Present in Array: false

2. Using Linear Search Algorithm - Naive approach

In the Linear search algorithm, iterate over the array using loops and compare each element of the array with the target value.

JavaScript 
const a = [10, 20, 30, 40, 50];
let n1 = 30,
	n2 = 45;
    
function check(value) {
	for (let i = 0; i < a.length; i++) {
		if (a[i] == value)
        // return if the value is found
        return value + " is present";
	}
	return value + " is not present";
}

console.log(check(n1));
console.log(check(n2));

Output
30 is present in the array.
45 is not present in the array.

3. 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.

JavaScript 
const a = [10, 20, 30, 40, 50];
let n = 40;
    
// Getting the index of element
const index = a.indexOf(n)

if ( index >= 0)
    console.log(n + " is present at", index, "index");
else
    console.log(n + " is not present.");

Output
40 is present at 3 index

4. Using Binary Search

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

JavaScript 
const a = [10, 20, 30, 40, 50];
let n1 = 30,
	n2 = 45;

// Function to implement binary search
function bsearch(arr, l, r, x) {
    if (r >= l) {
    	// Devide array into 2 parts
        let mid = l + Math.floor((r - l) / 2);
		// If found then retrun index
        if (arr[mid] == x)
            return mid;
            
		// Apply Binary Search on Left part
        if (arr[mid] > x)
            return bsearch(arr, l, mid - 1, x);
            
		// Apply Binary Search on Right part
        return bsearch(arr, mid + 1, r, x);
    }
	
    // If not found return -1
    return -1;
}
    
// To check if 30 is present or not
console.log("Is "+ n1 +" present? " + (bsearch(a, 0, a.length, n1) != -1));

// To check if 45 is present or not
console.log("Is "+ n2 +" present? " + (bsearch(a, 0, a.length, n2) != -1));

Output
Is 30 present? true
Is 45 present? false

5. Using filter() Method

The filter() method is used with the array to pull out the desired element from the array. We first create the array and use the filter method on an array with a method that checks element is present or not. If the element is present in the array it returns an array with an element else returns an empty array. 

JavaScript 
const a = [10, 20, 30, 40, 50];
let n1 = 30,
	n2 = 45;

function check(value) {
	
    // Filter out the values from array
    let filterArr = a.filter(x => x == value);
    
    // If there is at least one element in array 
    if (filterArr.length)
        return value + " is present in the array.";

    return value + " is not present in the array.";
}
console.log(check(n1));

console.log(check(n2));

Output
30 is present in the array.
45 is not present in the array.

6. Using the find() Method

The array find() method in JavaScript returns the first element in an array that satisfies the provided testing function. If no elements satisfy the condition, it returns undefined. By checking if the result is not undefined, you can determine if the value exists in the array.

JavaScript 
const a = [10, 20, 30, 40, 50];
let n = 45;

// Check the if the return value is undefined
const result = a.find(element => element === n) !== undefined;

console.log(result);

Output
false

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JavaScript - Create an Object From Two Arrays
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