Counting the occurrences / frequency of array elements

You can use an object to hold the results:

const arr = [5, 5, 5, 2, 2, 2, 2, 2, 9, 4];
const counts = {};

for (const num of arr) {
  counts[num] = counts[num] ? counts[num] + 1 : 1;
}

console.log(counts[5], counts[2], counts[9], counts[4]);

So, now your counts object can tell you what the count is for a particular number:

console.log(counts[5]); // logs '3'

If you want to get an array of members, just use the keys() functions

keys(counts); // returns ["5", "2", "9", "4"]