vanillahofs.js

const numbers = [ 2, 4, 8, 9 ]
const addTwo = number => number + 1
const isMoreThan5 = number => number > 5
const result =  
  //numbers.filter(isMoreThan5)
  filterArray(isMoreThan5, numbers)
  //mapArray(addTwo, numbers
result

function filterArray(predicate, array) {
  let filteredArray = []
  for(let i = 0; i < array.length; i++) {
    const currentItem = array[i]
    if(predicate(currentItem)) {
      filteredArray.push(currentItem)
    }
  }
  return filteredArray
}

function mapArray(transform, array) {
  let transformedArray = []
  for(let i = 0; i < array.length; i++) {
    transformedArray.push(transform(array[i]))
  }
  return transformedArray
}