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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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