Question

How to count duplicate elements in array with JavaScript

Answer 1

const object = {};

const array = [3, 5, 9, 1, 7, 8, 1, 9, 0, 3, 9];

array.forEach(function (x) { object[x] = (object[x] || 0) + 1; });

let count = 0;

for (const val in object) {
    if (object[val] >= 2) {
        count++;
    }
}


console.log(count);


 
 
 
/*
run:
 
3
 
*/

 

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