find-duplicates-in-array-alternative.js

// Find duplicates in an array of ints
// IMO, a bit messier/complicated than should be. But it works.
function findDupes(arr) {
	var counted = arr.reduce((all, item) => {
						all[item] = (all[item] || 0) + 1;
						return all;
  }, {});
	
	return Object.keys(counted).filter(x => counted[x] > 1).map(x => parseInt(x);
}