partition.js

function partition(inputArray, callback) {
  const result = {};
  for (const [indexOfValue, value] of inputArray.entries()) {
    const propertyKey = callback(value, indexOfValue);
    if (propertyKey === null || propertyKey === '') {
      continue;
    }
    if (!{}.hasOwnProperty.call(result, propertyKey)) {
      result[propertyKey] = [];
    }
    result[propertyKey].push(value);
  }
  return result;
}


const arr = [1, -5, 4, 5, -2]
const {negative, nonNegative} = partition(arr,
  elem => elem < 0 ? 'negative' : 'nonNegative');
console.log(negative);
  // [ -5, -2 ]
console.log(nonNegative);
  // [ 1, 4, 5 ]


const input = [
  {name: 'John', isLocal: true},
  {name: 'Jane', isLocal: false},
  {name: 'Charlie', isLocal: true}
];
const {local, global} = partition(input,
  (elem) => elem.isLocal ? 'local' : 'global');
console.log(local);
  // [ { name: 'John', isLocal: true }, { name: 'Charlie', isLocal: true } ]
console.log(global);
  // [ { name: 'Jane', isLocal: false } ]