Let's write native JavaScript Array methods from scratch! Part 2 (Challenge)

Introduction

Hey, welcome back! Here is the sequel (Part 2) to the previous blog post. Are you ready for some more fun? 🔥

So here is the challenge!

Can you write the JavaScript Array methods listed below from scratch?

The Rules

Don't use prototype. Instead, take the array as the first argument/parameter.
Don't use other native JavaScript methods to solve the problems
Feel free to use the latest ECMAScript standards such as the rest operator, spread operator, default values, etc...
Pay attention to understand if a method modifies the original array or returns a new array! Or if anything is returned at all.
Don't look up the solutions until you really tried!

Array methods

The Solutions

forEach

function forEach(array, callback) {
  for(let i=0; i<array.length; i++) {
    callback(array[i], i, array)
  }
}

map

function map(array, callback) {
  const result = []

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

  return result
}

filter

function filter(array, callback) {
  const result = []

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

  return result
}

reduce

// here is my attempt, can you do better?
function reduce(array, callback, initialValue) {
  let accumulator = initialValue || array[0]

  if(initialValue === 0) {
    accumulator = 0
  }

  for(let i=0; i<array.length; i++) {
    if(initialValue === undefined && i === 0) {
      continue
    }

    accumulator = callback(accumulator, array[i], i, array)
  }

  return accumulator
}

find

function find(array, callback) {
  for(let i=0; i<array.length; i++) {
    if(callback(array[i], i, array)) {
      return array[i]
    }
  }
}

findIndex

function findIndex(array, callback) {
  for(let i=0; i<array.length; i++) {
    if(callback(array[i], i, array)) {
      return i
    }
  }

  return -1
}

some

function some(array, callback) {
  let flag = false

  for(let i=0; i<array.length; i++) {
    if(callback(array[i], i, array)) {
      flag = true
    }
  }

  return flag
}

every

function every(array, callback) {
  let flag = true

  for(let i=0; i<array.length; i++) {
    if(!callback(array[i], i, array)) {
      flag = false
    }
  }

  return flag
}

Parting words 👋

I hope you enjoyed the challenge as much as I did! 🎉. Feel free to provide any feedback including 🐛's. I would also love to see your codes, feel free to post them as comments. Thank you and adios.

fillup