JSFiddle - React, Tailwind, and code Playground
JavaScript
var arr = [1,2,3,4,1,2,4,5,1,2];
function countOfDuplicates() {
var temp = {};
var count = 1;
for (var i = 0; i < arr.length; i++) {
if (arr[i] in temp) {
count++;
[arr[i]] = count;
} else {
[arr[i]] = count;
}
// return temp;
}
return temp;
}