differentiate.js

const differentiate = (targetArray, filterFunction) => targetArray.reduce(([truthAcc, falseAcc], item, index, arr) => {
  if (filterFunction(item, index, arr)) {
    truthAcc.push(item)
  } else {
    falseAcc.push(item)
  }
  return [truthAcc, falseAcc]
}, [[], []])

module.exports = { differentiate }

differentiate.test.js

const { differentiate } = require('./differentiate.js')
test('Differentiate Works', () => {
  const inputArray = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
  const expectedEvenValues = [0, 2, 4, 6, 8, 10]
  const expectedOddValues = [1, 3, 5, 7, 9]
  const isEvenArrayFilter = number => number % 2 === 0
  const [evenValues, oddValues] = differentiate(inputArray, isEvenArrayFilter)
  expect(evenValues).toEqual(expect.arrayContaining(expectedEvenValues))
  expect(oddValues).toEqual(expect.arrayContaining(expectedOddValues))
})