What you can do with JavaScript Array methods

Nov 29, 2018

Even though, code implemented in for-loop may run faster, I prefer array methods and use them all the time.


I have a few good reasons to use them.

  1. Unlike a loop, the code is cleaner without the index variables and expressions(initialization, condition and final).
  2. Less side effects because it returns a new array. Original array is not modified. Except for Array.prototype.forEach, it performs the callback function directly on each item of the array.

Let's see what we can do with array methods!

Finding the sum of all numbers in an array

Let's start with for loop.

const numbers = [1, 2, 3, 4, 5, 6, 7, 8]
let sum = 0

for (let i = 0; i < numbers.length; i++) {
  sum += numbers[i]

Now we can do that in one line using Array.prototype.reduce.

const sum = numbers.reduce((acc, num) => acc + num, 0)

We can even reuse the function to add to two numbers like this

function add (a, b) {
  return a + b

const sum = numbers.reduce(add, 0)

add(2, 3)
add(8, 12)

Counting characters

Let's say we want to count the occurrence of each character in a string. I will try using for loop first.

const str = 'Winter is here'
const charMap = {}

// remove whitespace characters from string
const cleanStr = str.toLowerCase().replace(/\s*/g, '')

// We will store each characters as an object key
// and its occurrence as the value
for (let i = 0; i < cleanStr.length; i++) {
  if (charMap[cleanStr[i]]) {
    // The character already exists, so we will count up one
    charMap[cleanStr[i]] += 1
  } else {
    // Initialize the new character count with one
    charMap[cleanStr[i]] = 1

charMap // { w: 1, i: 2, n: 1, t: 1, e: 3, r: 2, s: 1, h: 1 }

Now let's try to do that using reduce. I will assume that input string is in lowercase and that there is no whitespace characters.

const charMap = cleanStr.split('').reduce((acc, char) => {
  acc[char] = acc[char] ? acc[char] + 1 : 1
  return acc
}, {})

This time I am using ternary operator instead of if-else condition statement. Both of them serve the same thing.

One obvious thing here is that with reduce, we don't need to care about indexes at all.

Thanks for reading! Stay awesome and keep on hacking! 😍