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

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.

Method 1: Brute Force approach

• 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

<script>
    // Declare two array
    const array1 = ['a', 'b', 'c', 'd'];
    const 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))
</script>

Output:

false

Method 2:

• 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

<script>
    // Declare Two array
    const array1 = ['a', 'd', 'm', 'x'];
    const 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
                    const 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))
</script>

Output:

false

Method 3:

• 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 returns false

javascript

<script>
    // Declare two array
    const array1= ['a', 'b', 'x', 'z'];
    const 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))
</script>

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.