Get all values that have a max value under a getter

argmaxall.js

const a = [
  { a: 'one', b: 4 },
  { a: 'two', b: 1 },
  { a: 'three', b: 4 },
  { a: 'four', b: 2 }
];

function argmaxAll(getterFunction, arr) {
  return reduce(
    ([max, arr], curr) => {
      const currVal = getterFunction(curr);
      if (currVal > max) {
        return [currVal, [curr]];
      }
      if (currVal === max) {
        return [currVal, [...arr, curr]];
      }
      return [max, arr];
    },
    [0, []]
  )(arr)[1];
}

console.log(argmaxAll(get('b'), a));