# 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

1.  [forEach](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach) [⬇](#foreach)
2.  [map](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map) [⬇](#map)
3.  [filter](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter)  [⬇](#filter)
4.  [reduce](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce) [⬇](#reduce)
5.  [find](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/find) [⬇](#find)
6.  [findIndex](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/findIndex) [⬇](#findindex)
7.  [some](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/some) [⬇](#some)
8.  [every](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/every) [⬇](#every)


 

## The Solutions

 

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

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

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

  return result
}
``` 

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

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

  return -1
}
```

### some
```js
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
```js
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
}
```

&nbsp;

## 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. 

&nbsp;