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5 easy ways to get started with JavaScript .reduce()

As a completely new developer, my favorite JavaScript tools were .map() and for loops. But recently, I've been determined to understand more complex methods like .reduce.

Working through the Callbacks & Higher-order Functions challenges in CSX has been the perfect introduction to reduce, which was intimidating for me to get started with. But reduce is a powerful method and definitely worth the effort.

The first .reduce() method I was exposed to was via MDN
arr.reduce(callback(accumulator, currentValue[, index[, array]])[, initialValue])
The W3Schools definition was better, but not by much.

So what's the best way to get over this intimidation factor?

1) start small with basic examples

  • Most newbies are familiar with using .reduce() to aggregate the elements in an array
const theOG = (array) => {
  return array.reduce((acc, el) => {
    return acc + el
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2) remove any confusing terminology-- accumulator? What callback?

  • I played with simple reduce applications using just x and y.
  • But it might make more sense for you to use total and current or total and item
  • Doesn't this syntax look familiar?
return array.reduce((x, y) =>  x + y % 2)
return array.reduce((x, y) =>  x - y)
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3) console.log a lot

  • If you're not sure what reduce is doing, console.log and see how that matches with your expectation.
const reduces = (array) => {
return array.reduce((acc, num) => {
  console.log(acc, num)
  return acc + num
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4) add other arguments and console.log those

array.reduce((acc, num, index, array) => {
    console.log(num, index)
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5) practice + repetition

  • Challenge yourself to solve different problems using .reduce() instead of the more obvious loops or methods.
  • Solve the same problems over and over until they become second nature
  • For me, the CSX challenges did a great job of that, but you can also make up your own challenges

As with every topic, FreeCodeCamp has a straightforward article you can reference when stuck.

You can also view my reduce challenges here

Top comments (2)

torianne02 profile image
Tori Crawford

These are great tips for any JavaScript array method! I love it. Great post.

jasterix profile image