My implementation of Map, Filter and Reduce <3

map-filter-reduce.js

Array.prototype.map = function (callback) {
  const result = []

  for (let i = 0; i < this.length; i++) {
    result.push(callback(this[i], i, this))
  }

  return result
}

Array.prototype.filter = function (callback) {
  const result = []

  for (let i = 0; i < this.length; i++) {
    if (callback(this[i], i, this)) {
      result.push(this[i])
    }
  }

  return result
}

Array.prototype.reduce = function (callback, initial = 0) {
  let accumulator = initial

  for (let i = 0; i < this.length; i++) {
    accumulator = callback(accumulator, this[i], i, this)
  }

  return accumulator
}