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JavaScript: Understanding the Weird Parts (Udemy.com)

The advanced JavaScript course that has launched thousands of careers and keeps developers coming back every year.

4.8
49,462 reviews

Created by: Anthony Alicea

Last updated December 2025

Our take

Based on the ratings of 49,462 students, a sample of their written reviews and the syllabus, as the course stood in December 2025. No course pays to be reviewed.

Anthony Alicea's course is 12.6 hours and 92 lectures about what JavaScript is actually doing under the hood. It covers execution contexts, types and operators, objects and functions, and prototypal inheritance. Later it reads through jQuery's source and builds a small framework. It asks only for basic JavaScript, meaning variables, loops and simple functions. That makes it a second course, not a first one. About 200,000 students have taken it, and it holds 4.8 stars across roughly 49,000 reviews.

Reviewers like the clarity most. Alicea's teaching gets described as clear, with explanations that are easy to visualize, and a Java full stack engineer says it finally explained how JavaScript works under the hood. The complaints are consistent. The pace is slow enough that two reviewers suggest watching at 1.5x. One senior developer says only the first three or four sections felt advanced. Another reviewer wanted more visuals, since the videos are mostly voice and code. One experienced Java developer said they lost the thread after the jQuery sections.

The course was last updated in December 2025, but it was first published in 2015 and some reviewers say it shows its age. Others point out that the ideas still apply to current JavaScript, and that let, const and arrow functions sit near the end of the course. Expect to use the speed control. For anyone who can write basic JavaScript and wants closures, prototypes and scope to make sense, it is a solid pick. If you already know the language well, the early sections are the useful part.

Best forDevelopers who know basic JavaScript and want closures, prototypes and scope to finally make sense.
Skip it ifYou are already a senior JavaScript developer, or you want modern syntax taught first.

Pros

  • Explains execution contexts, closures and prototypes so the odd behavior makes sense
  • Reviewers call the explanations clear and easy to visualize
  • Reads jQuery source and builds a small framework to apply the ideas
  • Reviewers say the core concepts still apply to current JavaScript

Cons

  • Slow pace, with reviewers recommending 1.5x to 1.75x speed
  • Videos are mostly voice and code, with few visuals
  • Modern syntax like let and const comes late, and the style feels dated
If you want to learn something deep under the hood, this course helps a lot.
Unboundwill, a student

Suits people with basic JavaScript. Seniors may find the pace slow, and only the early sections get truly advanced.

Featured in our guide: The 9 Best Web Development Courses on Udemy in 2026

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What you will learn

  • Grasp how JavaScript works and it's fundamental concepts
  • Write solid, good JavaScript code
  • Understand advanced JavaScript concepts such as promises, async/await, closures, prototypal inheritance, IIFEs, classes, and much more.
  • Drastically improve your ability to debug problems in JavaScript.
  • Avoid common pitfalls and mistakes other JavaScript coders make
  • Understand the source code of popular JavaScript frameworks
  • Build your own JavaScript framework or library

Course content

13 sections · 92 lectures · 13 hours of video 1 quiz, 9 articles

  1. 1Getting Started 2 free previews6 lectures · 15 min
  2. 2Execution Contexts and Lexical Environments 13 free previews13 lectures · 1 quiz · 1.6 hours
  3. 3Types and Operators 11 free previews11 lectures · 1.3 hours
  4. 4Objects and Functions23 lectures · 4.5 hours
  5. 5Object-Oriented Javascript and Prototypal Inheritance4 lectures · 40 min
  6. 6Building Objects8 lectures · 1.1 hours
  7. 7Odds and Ends4 lectures · 19 min
  8. 8Examining Famous Frameworks and Libraries4 lectures · 52 min
  9. 9Let's Build a Framework / Library!8 lectures · 49 min
  10. 10EXTRA: TypeScript, ES6, and Transpiled Languages2 lectures · 5 min

Who it is for

The instructor says it suits

  • Those with basic JavaScript skills who wish to improve
  • Experienced coders coming from other programming languages
  • New and experienced JavaScript coders who want to deepen their understanding of the language
  • Anyone who has found concepts just as object prototypes, closures, and other advanced concepts difficult to learn
  • Those who have suffered surprising errors while writing JavaScript, and want to learn why and how to avoid them
  • Those interested in building their own frameworks, or being better able to learn from the source code of other well-known frameworks and libraries

What you need before you start

  • Basic Javascript knowledge (variables, loops, and basic functions - that's all the course expects you to know!)
  • A browser and text editor

How it compares

Against the other 239 rated Udemy courses in JavaScript on CourseDuck:

  • Rating4.8 out of 5higher than 93% of them
  • Reviews49,462#2 of 240 by number of reviews
  • Length12.6 hourslonger than 77% of them
  • Last updatedDecember 2025more recently than 84% of them

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Course Description

Javascript is the language that modern developers need to know, and know well. Truly knowing Javascript will get you a job, and enable you to build quality web and server applications.NOTE: This course includes information on ECMAScript 6 (ES6) the next version of Javascript!In this course you will gain a deep understanding of Javascript, learn how Javascript works under the hood, and how that knowledge helps you avoid common pitfalls and drastically improve your ability to debug problems. You will find clarity in the parts that others, even experienced coders, may find weird, odd, and at times incomprehensible. You'll learn the beauty and deceptive power of this language that is at the forefront of modern software development today.This course will cover such advanced concepts as objects and object literals, function expressions, prototypical inheritance, functional programming, scope chains, function constructors (plus new ES6 features), immediately invoked function expressions (IIFEs), call, apply, bind, and more.We'll take a deep dive into the source code of popular frameworks such as jQuery and Underscore to see how you can use your understanding of Javascript to learn (and borrow) from other's good code.Finally, you'll learn the foundations of how to build your own Javascript framework or library.What you'll learn in this course will make you a better Javascript developer, and improve your abilities in AngularJS, NodeJS, jQuery, React, Ember, MongoDB, and all other Javascript-based technologies!Learn to love Javascript, and code in it well.Note: In this course you'll also get downloadable source code. You will often be provided with 'starter' code, giving you the base for you to start writing your code, and 'finished' code to compare your code to.Who this course is for:Those with basic Javascript skills who wish to improveExperienced coders coming from other programming languagesNew and experienced Javascript coders who want to deepen their understanding of the languageAnyone who has found concepts just as object prototypes, closures, and other advanced concepts difficult to learnThose who have suffered surprising errors while writing Javascript, and want to learn why and how to avoid themThose interested in building their own frameworks, or being better able to learn from the source code of other well-known frameworks and libraries
Read More All Levels All Levels product length iconTime: 12.6h

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Instructor Details

Anthony Alicea

Newly married in Cleveland Ohio, Tony is primarily focused these days on trying to be a good husband. While inexperienced at that, he's quite experienced in all things web. Tony has been programming since he was 12 years old, and got into web sites and web application development at 16. After graduating with a Computer Science degree from Case Western Reserve University, Tony continued with that interest as a Microsoft certified software application developer and architect, database designer, and user interface designer. His experience has ranged across technologies such as HTML5, CSS3, ASP .NET MVC, JavaScript, jQuery, KnockoutJS, AngularJS, NodeJS, LESS, Bootstrap, SQL, Entity Framework and more. He believes strongly that deeply understanding any topic allows you to properly learn it and, even more importantly in a real-world environment, quickly overcome problems. He also has a deep interest in human nature and behavior, and how that impacts human-computer interaction. This interest translated into extending his career into user experience design and usability research. Another link in the chain is his 25 years of experience in public speaking and teaching, both in front of large groups and as a one-on-one private instructor. Putting all these pieces together, he has spent his career listening to a client need, designing a database and software to meet that need, building it, testing it, teaching others how to use it, then improving user experience by watching people actua

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Reviews

4.8

49,462 ratings on Udemy

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By Uday Kumar on 7/4/2019

Awesome Course - Which every Javascript Programmer should take up to understanding What is JavaScript!.

By Justin Missingham on 7/4/2019

I\'ve had SO MANY many ''Ah HAH!'' moments on this course. I\'ve read a tonne of books but still never really managed to piece together my (lack of!) knowledge of JavaScript into little more than poorly educated guesswork. I really now know SO MUCH about what JavaScript is doing when it\'s doing its thing. Thank you, thank you, THANK YOU. Great course. Highly recommended to all that have nearly got JavaScript (my first language so I\'ve no idea what\'s weird!) but can\'t tell why they haven\'t.\nP.S. I NEVER write reviews but I think this course really deserves it.

By Kaspars on 7/3/2019

Wery good explanation in details, what gave strong basis of understanding the program.

By Krishn Mohan Gandhi on 7/3/2019

I loved the teaching ethics of instructor and giving stress on understanding the basic (which others say weird ).\nI really loved some of basic and core topics like\nScope chain, IIFE, Closure, Execution context, and the lexical environment which sets my inclination towards javascript. \nI would love to understand some ES-6 feature like arrow function and this, ES-6 classes and much more.\nThank You, Tony,

By Andrew Faulkner on 7/3/2019

It helped get ready for the course with ease

By Raghu Venkatesh on 7/2/2019

The way the instructor explains the concepts makes them look easy.

By Cazzoli Algisto on 7/2/2019

Very useful course to understand the ''under the hood'' JavaScript\'s concepts

By Yeshwanth Kadri on 7/1/2019

JavaScript has been one of the toughest languages to learn, the introduction itself makes me comfortable. There are a lot of people teaching the codes, but no one teaches what really goes behind it and why. Great Intro indeed.

By CounterBean on 7/1/2019

Intresting

By Nes Abadiano on 6/30/2019

So far the course is exciting to watch!

By Cesar Martinez on 6/30/2019

Helped me to finally grasp concepts that remained cryptic to me in JS for a long time. I know I'll be returning to my notes on this course for years to come.

By N ET on 6/30/2019

The teacher is ... amazing. Covers most topics very clearly with his explanations and the graphical explainers are also very useful. I'd give this a 4.5 rating overall because it's just better than everything else I've seen for people who are native English speakers. I would love it if there were some in-context graphics, maybe some overlay drawings (sketch lines on top of the code, arrows, etc) supporting the verbal explanations, but that might just be wishful thinking.

Showing 12 of 369 reviews

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Overall Score : 96 / 100

JavaScript: Understanding the Weird Parts
Visit course on Udemy Write a review
  • Video Duration: icon 12.6h
  • Price: $149.99
  • Provider: icon Udemy
  • Updated: icon December 2025
  • Level: All Levels All Levels
  • Language: icon English
  • Certificate: icon Yes
  • Lectures:92 in 13 sections
  • Practice:1 quiz
  • Students:199,600
  • Subtitles:22 languages
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