You Don't Know JS Yet: The Unbooks
Previously Unpublished 2nd-Ed Book Content (Raw & Uncut)
You Don’t Know JS: The Unbooks is the final, draft-edition release of the second edition series—featuring the complete but unedited drafts of Book 3: Objects & Classes and Book 4: Types & Grammar, plus two bonus chapters reflecting on the “lost” books that were never written. This is the raw, honest conclusion to You Don’t Know JS Yet—a gift for readers who still care about deeply understanding JavaScript.
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You Don’t Know JS: The Unbooks is the final, draft-edition release of the second edition series—featuring the complete but unedited drafts of Book 3: Objects & Classes and Book 4: Types & Grammar, plus two bonus chapters reflecting on the “lost” books that were never written. This is the raw, honest conclusion to You Don’t Know JS Yet—a gift for readers who still care about deeply understanding JavaScript.
About
About the Book
You Don’t Know JS Yet: The Unbooks is a special, draft-edition release collecting the final remaining content from the second edition of the You Don’t Know JS Yet series. It includes the complete, previously unpublished drafts of Book 3: Objects & Classes and Book 4: Types & Grammar—books that were written in full but never formally edited or released for publication.
These chapters reflect the same in-depth exploration and care you’ve come to expect from the series, just presented here in their raw, unedited, unpolished form. They’re readable, structurally complete, and technically solid—offered honestly as-is.
This release also includes two bonus chapters on the “lost” volumes that were never written: Book 5: Sync & Async and Book 6: ES.Next & Beyond. These reflective essays explain what those books were meant to be, why they were ultimately abandoned, and what insights remain worth sharing. This is a project for the completists, the curious, and anyone who still cares deeply about understanding JavaScript, not just using it.
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Author
About the Author
Kyle Simpson
Kyle Simpson is a web-oriented software engineer, widely acclaimed for his "You Don't Know JS" book series and nearly 1M hours viewed of his online courses. Kyle's superpower is asking better questions, who deeply believes in maximally using the minimally-necessary tools for any task. As a "human-centric technologist", he's passionate about bringing humans and technology together, evolving engineering organizations towards solving the right problems, in simpler ways. Kyle will always fight for the people behind the pixels.
Episode 166
An Interview with Kyle Simpson
Contents
Table of Contents
Preface
- Objects & Classes (Unbook 3)
Chapter 1: Object Foundations (Objects & Classes)
- About This Book
- Objects As Containers
- NOTE
- TIP
- Defining Properties
- WARNING
- NOTE
- NOTE
- NOTE
- Accessing Properties
- WARNING
- NOTE
- Assigning Properties
- WARNING
- Deleting Properties
- Determining Container Contents
- Temporary Containers
- Containers Are Collections Of Properties
Chapter 2: How Objects Work (Objects & Classes)
- Property Descriptors
- WARNING
- Object Sub-Types
- NOTE
- WARNING
- Object Characteristics
- Extending The MOP
[[Prototype]]Chain- WARNING
- NOTE
- NOTE
- WARNING
- Objects Behavior
Chapter 3: Classy Objects (Objects & Classes)
- When Should I Class-Orient My Code?
- Keep It
classy - NOTE
- NOTE
- Class Instance
this - TIP
- Class Extension
- WARNING
- NOTE
- Static Class Behavior
- NOTE
- NOTE
- WARNING
- TIP
- Private Class Behavior
- TIP
- WARNING
- Class Example
- NOTE
Chapter 4: This Works (Objects & Classes)
- This Aware
- This Is It!
- NOTE
- WARNING
- NOTE
- TIP
- WARNING
- TIP
- An Arrow Points Somewhere
- NOTE
- NOTE
- TIP
- TIP
- NOTE
- TIP
- NOTE
- NOTE
- Variations
- NOTE
- Stay Aware
Chapter 5: Delegation (Objects & Classes)
- Preamble
- What’s A Constructor, Anyway?
- TIP
- Ditching Class Thinking
- Delegation Illustrated
- TIP
- Composing Peer Objects
- Why This?
- Types & Grammar (Unbook 4)
Chapter 1: Primitive Values (Types & Grammar)
- Value Types
- WARNING
- TIP
- Empty Values
- NOTE
- NOTE
- WARNING
- WARNING
- Boolean Values
- String Values
- NOTE
- TIP
- NOTE
- NOTE
- TIP
- TIP
- Number Values
- NOTE
- WARNING
- NOTE
- NOTE
- NOTE
- TIP
- NOTE
- TIP
- WARNING
- BigInteger Values
- WARNING
- WARNING
- NOTE
- Symbol Values
- WARNING
- NOTE
- Primitives Are Built-In Types
Chapter 2: Primitive Behaviors (Types & Grammar)
- Primitive Immutability
- WARNING
- NOTE
- NOTE
- Primitive Assignments
- NOTE
- String Behaviors
- NOTE
- NOTE
- NOTE
- NOTE
- NOTE
- NOTE
- NOTE
- WARNING
- Number Behaviors
- NOTE
- TIP
- NOTE
- WARNING
- WARNING
- Primitives Are Foundational
Chapter 3: Object Values (Types & Grammar)
- Types of Objects
- Plain Objects
- Fundamental Objects
- WARNING
- NOTE
- Other Built-in Objects
- Arrays
- Regular Expressions
- Functions
- Proposed: Records/Tuples
Chapter 4: Coercing Values (Types & Grammar)
- Coercion: Explicit vs Implicit
- Abstracts
- WARNING
- WARNING
- NOTE
- WARNING
- WARNING
- Concrete Coercions
- NOTE
- NOTE
- WARNING
- WARNING
- WARNING
- WARNING
- WARNING
- WARNING
- Coercion Corner Cases
- Type Awareness
- NOTE
- NOTE
- WARNING
- NOTE
- TIP
- TIP
- What’s Left?
- Sync & Async (Unbook 5)
Chapter 1: Lost Book (Sync & Async)
- The Plan
- The Reality
- That said…
Chapter 2: Random Musings (Sync & Async)
- Synchronous Iteration
- Asynchronous Iteration
- ES.Next & Beyond (Unbook 6)
Chapter 1: Lost Book (ES.Next & Beyond)
- However…
Chapter 2: The Bright Parts (ES.Next & Beyond)
- Nullish
- Warning
- Synchronous Iteration Helpers
- Readable Numbers
- Named Regex Capture Groups
- Promise Expansions
- Second Edition Thank Yous
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