Write a JavaScript program to group the elements of a given array based on the given function

const group_By = (arr, fn) =>
  arr.map(typeof fn === 'function' ? fn : val => val[fn]).reduce((acc, val, i) => {
    acc[val] = (acc[val] || []).concat(arr[i]);
    return acc;
  }, {});
console.log(group_By([6.1, 4.2, 6.3], Math.sqrt)); 
console.log(group_By([6.1, 4.2, 6.3], Math.floor)); 
console.log(group_By(['one', 'two', 'three'], 'length'));