get most occurring elements in array JavaScript

Question

I have an array that I want to get the most occurring elements,

First scenario

let arr1 = ['foo', 'foo', 'foo', 'bar', 'bar', 'bar', 'baz', 'baz']
let newArr = someFunc(arr1)

so in this case I want the new array to have the value

console.log(newArr) // ['foo', 'bar'] 

Because the value 'foo' and 'bar' was the most occurring element of the array

Second scenario

 let arr2 = ['foo', 'foo', 'foo', 'bar', 'baz']
 let newArr = someFunc(arr2)

so in this case I want the new array to have the value

console.log(newArr) // ['foo']

Because the value 'foo' was the most occurring element of the array

This is what I have tried and it will only get me one of the elements even if there are more than one element that occurs the same amount of times

newArr= arr.sort((a,b) =>
arr.filter(v => v===a).length
- arr.filter(v => v===b).length
).pop()

Answer 1

You can count the items with reduce and find the maximum occurring count. Then you can filter any keys that have that count:

let arr = ['foo', 'foo', 'foo', 'bar', 'bar', 'bar', 'baz', 'baz'];

let counts = arr.reduce((a, c) => {
  a[c] = (a[c] || 0) + 1;
  return a;
}, {});
let maxCount = Math.max(...Object.values(counts));
let mostFrequent = Object.keys(counts).filter(k => counts[k] === maxCount);

console.log(mostFrequent);