Using array.reduce method to count duplicate elements

 

const alphabets = [1,1,1,2,3,3,1,4,5];
const counts = alphabets.reduce((acc, current) => {
    if(acc[current]){
        acc[current] += 1;
    } else {
        acc[current] = 1;
    }
    return acc;
}, {});

console.log(counts); //{ '1': 4, '2': 1, '3': 2, '4': 1, '5': 1 }