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Web Development Beginner Bestseller

Modern JavaScript Array Methods in 45 Minutes

Replace every for-loop you write with the right array method, and know why.

Rated 4.5 out of 5 from 6 reviews 52 students

MH Created by Marcus Hale

  • Last updated August 2026
  • English
  • 45m of material
  • 6 lessons

What you will learn

6 concrete outcomes

Every bullet below is something you will have built, shipped or be able to explain by the time you finish the last lesson.

  • Reshape and filter data with map and filter instead of manual loops
  • Locate records with find, findIndex, findLast and includes
  • Validate collections with some and every in a single expression
  • Group and total data with reduce without fear
  • Flatten nested results using flat and flatMap
  • Avoid accidental mutation using toSorted, toReversed, toSpliced and with

Course curriculum

4 modules · 6 lessons · 45m of material

2 lessons running 15m in total. Each lesson ships with the finished source files and a short written recap, so you can follow along in your own editor and skim the module again later.

Lesson-by-lesson titles, code downloads and exercises live inside the course library you get access to straight after checkout.

2 lessons running 14m in total. Each lesson ships with the finished source files and a short written recap, so you can follow along in your own editor and skim the module again later.

Lesson-by-lesson titles, code downloads and exercises live inside the course library you get access to straight after checkout.

1 lesson running 9m in total. Each lesson ships with the finished source files and a short written recap, so you can follow along in your own editor and skim the module again later.

Lesson-by-lesson titles, code downloads and exercises live inside the course library you get access to straight after checkout.

1 lesson running 7m in total. Each lesson ships with the finished source files and a short written recap, so you can follow along in your own editor and skim the module again later.

Lesson-by-lesson titles, code downloads and exercises live inside the course library you get access to straight after checkout.

4 modules · 6 lessons

45m total length

Requirements

Short list, and deliberately so. If you meet these you can start today.

  • Basic JavaScript: variables, functions and arrays
  • A browser console or Node to run the snippets alongside the lessons

About this course

Array methods are the highest-leverage forty-five minutes a JavaScript beginner can spend. Most everyday data work is a map, a filter, a find or a reduce, and getting fluent with them removes a surprising amount of noise from your code.

This mini-course covers each method with a real task rather than a toy: map to reshape API responses, filter to apply user-selected criteria, find and findIndex to locate a record, some and every for validation, flatMap for nested results, and reduce for grouping and totals. The reduce lesson is deliberately long, because reduce is where most people give up, and it is shown alongside the loop it replaces until the shape is obvious.

The closing lesson covers mutation. Sort, reverse and splice change the original array, which causes real bugs in framework state. You will learn the copying alternatives added in recent JavaScript versions, toSorted, toReversed, toSpliced and with, and when each is worth using.

Topics covered

Frequently asked questions

Still unsure about something? Write to misteryjj100@gmail.com and a human answers, usually the same working day.

No, it is a focused mini-course on one topic. The JavaScript beginner path covers the language properly and this makes a good companion to it.

toSorted, toReversed, toSpliced and with are supported in all current browsers and Node 20 or newer. The lesson lists the exact support baseline.

Directly, and it improves there. Each lesson notes what TypeScript infers from the callback, and the copying methods pair well with readonly arrays because they never mutate the source.

Checkout is handled on our provider's secure payment page. The moment your payment clears we email your personal access link and access code to the address you used at checkout, and the same link appears in your account library. There is nothing to install and nothing to wait for.

Email misteryjj100@gmail.com within 14 days of your purchase, quote your order number, and we refund the full amount to your original payment method. No form to fill in and no questions about how much of the course you watched.

What students say

Reviews are written by people who bought this course. We publish the critical ones too.

4.5

Rated 4.5 out of 5

Course rating · 6 reviews

Rating distribution

  • 5 stars 67%
  • 4 stars 17%
  • 3 stars 17%
  • 2 stars 0%
  • 1 star 0%
  • NH

    Nour Haddad

    JavaScript developer

    Jun 2026
    Rated 5.0 out of 5

    Short and it sticks

    Watched it on a train and used it the same afternoon. The idea that all of these take a callback with the same three arguments is what turned a list I was trying to memorise into a family I now understand.
  • SA

    Selin Aydın

    Frontend developer

    Apr 2026
    Rated 5.0 out of 5

    reduce stopped scaring me

    Every other explanation starts by summing an array of numbers and then leaps to something baroque. This one builds up the shape of the accumulator first and the rest follows from it. I have reached for reduce twice this week without looking anything up.
  • MB

    Marco Bianchi

    Full-stack developer

    Dec 2025
    Rated 5.0 out of 5

    The copying methods were news to me

    I had no idea toSorted and toSpliced existed. Years of defensively spreading an array before sorting it, for no reason. Worth the forty-five minutes for that section alone.
  • EL

    Erik Lund

    CS student

    Sep 2025
    Rated 5.0 out of 5

    good use of forty-five minutes

    good use of forty-five minutes. some and every get explained against a form validation example rather than an array of integers, which is exactly why the difference between them stayed with me.
  • PJ

    Priyanka Joshi

    Web developer

    Jun 2025
    Rated 4.0 out of 5

    Wanted more on flatMap

    All correct and well judged for the length. flatMap gets about ninety seconds though, and of the whole set it is the one I understand least. I would happily have given up some of the map coverage to get it.
  • GS

    Gabriel Santos

    Self-taught, switching careers

    Mar 2025
    Rated 3.0 out of 5

    Understated prerequisites

    The listing says no prior experience is needed, and then chapter two is entirely comfortable with arrow functions, destructuring inside the callback parameters and implicit returns. If for-loops are honestly all you know, you will be pausing every thirty seconds. The material is good once you are past that barrier, but the description should say so.

Your instructor

MH

Marcus Hale

Web engineer and JavaScript educator

  • 259 students taught
  • 12 courses published
  • 4.7 instructor rating
  • JavaScript
  • TypeScript
  • React
  • Node.js

Marcus has shipped front ends for two ad-tech startups and one very large retailer, which taught him more about performance budgets than any blog post could. He teaches JavaScript and TypeScript from the runtime up — event loop first, framework second — then follows the same code through Node on the server side. Every one of his courses ends with a deployed application rather than a folder of exercises. He writes a weekly newsletter on browser performance.

See every course by Marcus Hale
$2 USD

One-time payment · lifetime access

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