Javascript : Find Duplicate in array using Object

 

 const arr = [4, 2, 7, 4, 2, 8, 4, 9];

 let duplicates = {};

 for (let i = 0; i < arr.length; i++) {

        if (duplicates[arr[i]]) {

            duplicates[arr[i]] = duplicates[arr[i]] + 1;

        } else {

            duplicates[arr[i]] = 1;

        }

 }

 console.log("Duplicates", duplicates);

 Output:

 Duplicates { '2': 2, '4': 3, '7': 1, '8': 1, '9': 1 }  

 Explanation:

1. We first initialize an empty object called `duplicates` to store the occurrence of each number

2. We then loop through the array and check if the current number is already present in the

`duplicates` object. If it is present, we increment its count by 1. If it is not present,

we add it to the `duplicates` object with a count of 1.