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

Last Updated : 20 May, 2019

Given two arrays containing array elements and the task is to check if two arrays contain any common elements then it returns True otherwise return 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 second array.
Loop through array1 and iterate it from beginning to the end.
Loop through array2 and iterate it from beginning to the end.
Compare each and every item from array1 to array2 and if it finds any common item then return true otherwise return false.

Example:

<script>
  
// Declare two array
const array1 = ['a', 'b', 'c', 'd'];
const array2 = ['k', 'x', 'z'];
  
// Function definiton 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; 
}
  
document.write(findCommonElement(array1, array2))
</script>                    

Output:

false

Time Complexity: O(M * N)

Method 2:

Create an empty object and loop through 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 second array and check if elements in the second array exists on created object.
If element exist then return true else return false.

Example:

<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;
}
  
document.write(findCommonElements2(array1, array2))
</script>                    

Output:

false

Time Complexity: O(M + N)

Method 3:

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

<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))
}
  
document.write(findCommonElements3(array1, array2))
</script>                    

Output:

true

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