Get get The Most Repetitive Item In Array

getTheMostRepetitiveItem.js

function getTheMostRepetitiveItem(items) {
  const itemCounts = items.reduce((storageObj, item) => {
    storageObj[item] = storageObj[item] || 0;
    storageObj[item] += 1;
    return storageObj;
  }, {});
  const sortedItems = Object.entries(itemCounts).sort(([keyA, valA], [keyB, valB]) => valB - valA);
  return sortedItems[0]?.[0];
}

function getTheMostRepetitiveItem(array) {
    let xx = array => (
        array.reduce(
            (acc, item) => {
                !(item in acc) ? acc[item] = 1 : acc[item]++;
                return acc;
            }
            , {})
    );
    let obj = xx(array);
    return Object.keys(obj).find(k => obj[k] === Math.max(...Object.values(obj)));
}

@alicivil
I think this is a good idea to move Math.max(...Object.values(obj)) to the outside of the find method to increase performance.
I also recommend to you use more readable and meaningful words for your variables and functions names.
And finally, I don't know why you are creating a new function named xx?