How to find if two arrays contain any common item in Javascript ?

In this article, we are given two arrays containing array elements and the task is to check if two arrays contain any common elements then it returns True otherwise returns False.

Examples:

Input: array1 = ['a', 'b', 'c', 'd', 'e']
       array2 = ['f', 'g', 'c']
Output: true
Input: array1 = ['x', 'y', 'w', 'z']
       array2 = ['m', 'n', 'k']
Output: false

There are many methods to solve this problem in JavaScript some of them are discussed below.

Methods to check the common items in arrays:

• Brute force approach: using JavaScript loops
• Creating a new JavaScript Object
• Using JavaScript Array.some() and .include() methods

Method 1: Brute Force approach: using JavaScript loops

• Compare each and every item from the first array to each and every item of the second array.
• Loop through array1 and iterate it from beginning to end.
• Loop through array2 and iterate it from beginning to end.
• Compare each and every item from array1 to array2 and if it finds any common item then return true otherwise return false.

Example: In this example, we will be using the above approach to find if two arrays contain any common item in Javascript.

javascript

// Declare two array
let array1 = ['a', 'b', 'c', 'd'];
let array2 = ['k', 'x', 'z'];

// Function definition with passing two arrays
function findCommonElement(array1, array2) {

    // Loop for array1
    for (let i = 0; i < array1.length; i++) {

        // Loop for array2
        for (let j = 0; j < array2.length; j++) {

            // Compare the element of each and
            // every element from both of the
            // arrays
            if (array1[i] === array2[j]) {

                // Return if common element found
                return true;
            }
        }
    }

    // Return if no common element exist
    return false;
}

console.log(findCommonElement(array1, array2))

Output

false

Method 2: Creating a new JavaScript Object

• Create an empty object and loop through the first array.
• Check if the elements from the first array exist in the object or not. If it doesn’t exist then assign properties === elements in the array.
• Loop through the second array and check if elements in the second array exist on created object.
• If an element exists then return true else return false.

Example: In this example, we will be using the above approach to find if two arrays contain any common item in Javascript.

javascript

// Declare Two array
let array1 = ['a', 'd', 'm', 'x'];
let array2 = ['p', 'y', 'k'];

// Function call
function findCommonElements2(arr1, arr2) {

    // Create an empty object
    let obj = {};

    // Loop through the first array
    for (let i = 0; i < arr1.length; i++) {

        // Check if element from first array
        // already exist in object or not
        if (!obj[arr1[i]]) {

            // If it doesn't exist assign the
            // properties equals to the
            // elements in the array
            let element = arr1[i];
            obj[element] = true;
        }
    }

    // Loop through the second array
    for (let j = 0; j < arr2.length; j++) {

        // Check elements from second array exist
        // in the created object or not
        if (obj[arr2[j]]) {
            return true;
        }
    }
    return false;
}

console.log(findCommonElements2(array1, array2))

Output

false

Method 3: Using JavaScript Array.some() and .include() methods

• Use the inbuilt ES6 function some() to iterate through each and every element of the first array and to test the array.
• Use the inbuilt function includes() with the second array to check if an element exists in the first array or not.
• If an element exists then return true else return false

Example: In this example, we will be using the above approach to find if two arrays contain any common item in Javascript.

javascript

// Declare two array
let array1 = ['a', 'b', 'x', 'z'];
let array2 = ['k', 'x', 'c']

// Iterate through each element in the
// first array and if some of them
// include the elements in the second
// array then return true.
function findCommonElements3(arr1, arr2) {
    return arr1.some(item => arr2.includes(item))
}

console.log(findCommonElements3(array1, array2))

Output

true

JavaScript is best known for web page development but it is also used in a variety of non-browser environments. You can learn JavaScript from the ground up by following this JavaScript Tutorial and JavaScript Examples.