Where to learn about reduce(), map(), and filter()?

Hello! When working on “Use the Rest Parameter with Function Parameters,” I looked at the solution and found that I needed to use reduce(). I started out on the Algorithms and Data Structures certificate brand new to JavaScript and never learned about these in the curriculum. Where can I go to learn about these and more similar functions?

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HI @NightFire222 !

Welcome to the forum!

map, reduce and filter are more formally introduced in the functional programming section

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Thank you! Should I continue these sections in order, or is there an order you’d recommend I do the sections in?

I would continue to do them in order

Hey there!

In addition to the resources already shared I also found this multipart series very helpful when I was trying to wrap my head around these functions

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Those solutions are just possible solutions, they are not the solution and should not be taken as gospel. Don’t worry if your code looks a little different.


Thank you. I think one problem I am having with the ES6 lessons is that I simply have no idea what I’m doing.


I don’t remember where it is in the curriculum, but at some point they have you recreate all of the those higher-order array methods with for loops. As long as you understand for loops, you could recreate them all.

// sum elements of arr
const reduceSum = arr.reduce((a, b) => a + b, 0);

// also, sum elements of arr
let forLoopSum = 0;
for (let i = 0; i < arr.length; i++) {
  forLoopSum += arr[i];

What I mean to say is, don’t worry about it!


i myself like to understand the functions i use so here i found the full description for the .reduce() and the parameters it needs, scroll down till you find SYNTAX

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