JavaScript Array Method Algorithm

Have you ever wondered how Array methods work under the hood? Do you wish to know what algorithms they use to work their magic? Well I have, and if you're are like me then you have too. So I decided to recreate them to discover what they are actually made of. Please leave a star on this repository if you find this helpful in any way.

.pop()

The pop method removes the last item of the array and returns that item.

ALGORITHM

• Create a new empty array
• Loop over current array except the last item
• Assign the looped over item(s) from the current array to the new array
• Overwrite the item(s) of the current array with the item(s) of the new array
• Return the last item of the current array that was added

let arr = ["Montserrado", "Margibi", "Lofa", "Nimba", "Maryland", "Rivercess", "Gbarpolu", "Bomi", "Sinoe"];

const pop = array => {
  let newArray = [];
  for (let i=0; i<array.length -1; i++){
      newArray[i] = array[i];
  }
  arr = newArray;
  return array[array.length -1];
}

pop(arr);

RESULT

"Sinoe"

.push()

The push method adds a new item to the end of an array and returns the new length of the array.

ALGORITHM

• Check to see if an item was passed or not
• Add the new item to the end of the array
• Return the length of the array

let arr = ["Montserrado", "Margibi", "Lofa", "Nimba", "Maryland", "Rivercess", "Gbarpolu", "Bomi", "Sinoe"];

const push = (array, item) => {
  if (item !== undefined) {
    array[array.length] = item;
  }
  return array.length;
} 

push(arr, "Grand Kru");

RESULT

10

.shift()

The shift method removes the first item of the array and returns that item.

ALGORITHM

• Create a new empty array
• Loop over current array except the first item
• Assign the looped over item(s) from the current array to the new array
• Overwrite the item(s) of the current array with the item(s) of the new array
• Return the first item of the current array that was removed

let arr = ["Montserrado", "Margibi", "Lofa", "Nimba", "Maryland", "Rivercess", "Gbarpolu", "Bomi", "Sinoe"];

const shift = (array) => {
  let newArray = []; 
  for (let i=1; i<array.length; i++){
    newArray[i -1] = array[i];
  }
  arr = newArray;
  return array[0];
} 

shift(arr);

RESULT

"Montserrado"

.unshift()

The unshift method adds an item to the beginning of the array and returns the new length of the array.

ALGORITHM

• Check to see if an item was passed or not
• Create a new array and assign the new item to it
• Loop over the current array and add the items to the new array
• Overwrite the current array with the new array
• Return the new length of the current array

let arr = ["Montserrado", "Margibi", "Lofa", "Nimba", "Maryland", "Rivercess", "Gbarpolu", "Bomi", "Sinoe"];

const unshift = (array, item) => {
  if (item !== undefined){
    let newArray = [item];
    for (let i=0; i<array.length; i++){
      newArray[i+1] = array[i];
    }
    arr = newArray;
  }
  return arr.length;
}

unshift(arr, "Grand Kru");

RESULT

10

.map()

The map method runs a function on each item of the current array and returns the result in a new array.

ALGORITHM

• Create a new array
• Loop over the current array
• Run an IIFE on each item of the current array and add the return value to the new array
• Return the new array

let arr = ["Montserrado", "Margibi", "Lofa", "Nimba", "Maryland", "Rivercess", "Gbarpolu", "Bomi", "Sinoe"];

const map = array => {
  let newArray = [];
  for (let i=0; i<array.length; i++){
    newArray[i] = function() {
      return array[i] + " County";
    }();
  }
  return newArray;
}

map(arr);

RESULT

['Montserrado County', 'Margibi County', 'Lofa County', 'Nimba County', 'Maryland County', 'Rivercess County', 'Gbarpolu County', 'Bomi County', 'Sinoe County']

.filter()

The filter method

let arr = ["Montserrado", "Margibi", "Lofa", "Nimba", "Maryland", "Rivercess", "Gbarpolu", "Bomi", "Sinoe"];

RESULT

.reduce()

The reduce method

let arr = ["Montserrado", "Margibi", "Lofa", "Nimba", "Maryland", "Rivercess", "Gbarpolu", "Bomi", "Sinoe"];

RESULT

.reduceRight()

The reduceRight method

let arr = ["Montserrado", "Margibi", "Lofa", "Nimba", "Maryland", "Rivercess", "Gbarpolu", "Bomi", "Sinoe"];

RESULT

.slice()

The slice method

let arr = ["Montserrado", "Margibi", "Lofa", "Nimba", "Maryland", "Rivercess", "Gbarpolu", "Bomi", "Sinoe"];

RESULT

.splice()

The splice method

let arr = ["Montserrado", "Margibi", "Lofa", "Nimba", "Maryland", "Rivercess", "Gbarpolu", "Bomi", "Sinoe"];

RESULT

.forEach()

The forEach method

let arr = ["Montserrado", "Margibi", "Lofa", "Nimba", "Maryland", "Rivercess", "Gbarpolu", "Bomi", "Sinoe"];

RESULT

.includes()

The includes method

let arr = ["Montserrado", "Margibi", "Lofa", "Nimba", "Maryland", "Rivercess", "Gbarpolu", "Bomi", "Sinoe"];

RESULT

.find()

The find method

let arr = ["Montserrado", "Margibi", "Lofa", "Nimba", "Maryland", "Rivercess", "Gbarpolu", "Bomi", "Sinoe"];

RESULT

.some()

The some method

let arr = ["Montserrado", "Margibi", "Lofa", "Nimba", "Maryland", "Rivercess", "Gbarpolu", "Bomi", "Sinoe"];

RESULT

.every()

The every method

let arr = ["Montserrado", "Margibi", "Lofa", "Nimba", "Maryland", "Rivercess", "Gbarpolu", "Bomi", "Sinoe"];

RESULT

.sort()

The sort method

let arr = ["Montserrado", "Margibi", "Lofa", "Nimba", "Maryland", "Rivercess", "Gbarpolu", "Bomi", "Sinoe"];

RESULT

.reverse()

The reverse method

let arr = ["Montserrado", "Margibi", "Lofa", "Nimba", "Maryland", "Rivercess", "Gbarpolu", "Bomi", "Sinoe"];

RESULT

.findIndex()

The findIndex method

let arr = ["Montserrado", "Margibi", "Lofa", "Nimba", "Maryland", "Rivercess", "Gbarpolu", "Bomi", "Sinoe"];

RESULT

.indexOf()

The indexOf method

let arr = ["Montserrado", "Margibi", "Lofa", "Nimba", "Maryland", "Rivercess", "Gbarpolu", "Bomi", "Sinoe"];

RESULT

.lastIndexOf()

The lastindexOf method

let arr = ["Montserrado", "Margibi", "Lofa", "Nimba", "Maryland", "Rivercess", "Gbarpolu", "Bomi", "Sinoe"];

RESULT

.concat()

The concat method

let arr = ["Montserrado", "Margibi", "Lofa", "Nimba", "Maryland", "Rivercess", "Gbarpolu", "Bomi", "Sinoe"];

RESULT

.join()

The join method

let arr = ["Montserrado", "Margibi", "Lofa", "Nimba", "Maryland", "Rivercess", "Gbarpolu", "Bomi", "Sinoe"];

RESULT