Answers for "how to find how many times duplicate number in array javascript"

duplicate an array in javascript n times

const makeRepeated = (arr, repeats) =>
  Array.from({ length: repeats }, () => arr).flat();
  
console.log(makeRepeated([1, 2, 3], 2));

counting duplicate values javascript

var counts = {};
your_array.forEach(function(x) { counts[x] = (counts[x] || 0)+1; });