The JavaScript Tool I'm using to demonstrate: ColorCode Etsy Merchandise store: 0:00 Intro Animation 3:13 Introduction 4:00 What is a Mutation? (Examples) 5:03 Immutability 6:07 Examples 8:51 Theory + Common patterns 10:11 React 12:45 Benefits 15:00 Your Instagram questions 18:35 Downsides and Performance concerns 19:28 Summary 20:40 Outro This is Episode 20 of the series 20 Things JavaScript Developers Should Know But Probably Don't, by Sina Jazayeri, Ever wondered why everyone talks about "immutability" in JavaScript — and what it actually means? In this video, we break it all down with real-world examples and a clean, practical approach. 🚀 Learn why mutating shared objects and arrays causes unexpected bugs, how immutability helps make your apps more reliable, and how concepts like cloning and reference tracking make modern frameworks like React work. We'll show you how to write immutable code, what pitfalls to watch for, and how to use modern tools like structuredClone to work safely with complex data. 🔥 Topics Covered: What is mutation in JavaScript? Why mutability causes unexpected side effects How to properly clone and update objects/arrays How React relies on immutability to detect changes When immutability is worth it — and when it isn't 👩‍💻 Example Highlights: Mutation problems with shared references Real-world draft editing bugs Spread operator vs structuredClone How to build your own tiny setState function in pure JavaScript Benefits (and trade-offs) of immutable thinking Understanding immutability is key to writing more predictable, debuggable, and scalable JavaScript — especially as your apps grow. If you enjoy learning about JavaScript concepts explained in a simple way, make sure to like, comment, and subscribe! 👍✨ Full playlist here: JavaScript Immutability from the series "20 Things JS Developers Should Know but Probably Don't" by , Sina Jazayeri *** Announcement *** Full JavaScript Mastery course is coming! Sign up for Early Access here: