const duplicateElements = (array) => {
for(let numbers of array) {
// code here
}
}
const numbers = [1,3,2,4,1,3,2];
duplicateElements(numbers);
// Output 4
With the JS function filter you can archive this. First you have to iterate your array. then check with the filter function how many times the current value is inside your array. If equal 1 then push to an result array.
const d = [];
const arr = [1,3,2,4,1,3,2]
arr.forEach((e) => {
if (arr.filter(x => x == e).length === 1) {
d.push(e);
}
})
console.log(d);