Answers for "how to find duplicate and how many times it occurs in js"

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; });

how to count duplicates in an array javascript

arr.reduce((b,c)=>((b[b.findIndex(d=>d.el===c)]||b[b.push({el:c,count:0})-1]).count++,b),[]);