An Elm Primer for React Developers
An Elm Primer for React Developers
The Best Way to Learn Real Functional Programming
About the Book
Elm is a functional programming language that compiles to JavaScript, and it offers something React can't: zero runtime exceptions, guaranteed. No null pointer errors. No "undefined is not a function". If your Elm code compiles, it works.
This book is your practical guide from React to Elm. Written by a staff developer working in a production codebase with 125,000+ lines of Elm, it shows you side-by-side comparisons, real-world patterns, and honest trade-offs. You'll see familiar React patterns translated to Elm's approach—state management, side effects, component architecture—and understand why Elm makes certain choices.
But here's the real value: Even if you never use Elm professionally, learning it will make you a better developer in any language. Elm is the fastest way to truly learn functional programming—not watered-down FP patterns, but real, uncompromising functional thinking. It's stricter than TypeScript, simpler than Haskell, and more practical than academic theory.
What you'll learn:
- The Elm Architecture (TEA)—the pattern that inspired Redux
- How compile-time guarantees prevent entire classes of bugs
- Pure functions, immutability, and explicit effects—FP concepts that transfer everywhere
- When to choose Elm (and when not to)
- How to integrate Elm widgets into existing React applications
- Real patterns from production codebases at scale
Who this book is for:
- React developers curious about functional programming
- Teams dealing with production bugs despite TypeScript
- Developers tired of debugging state management issues
- Anyone who wants to level up their programming skills
Your React knowledge is your advantage here. If you understand reducers and immutability patterns, you're already halfway to Elm. This book meets you where you are and shows you what's possible with different trade-offs.
Whether you adopt Elm or not, you'll come away with insights that make you better at React, TypeScript, and any language where clarity matters.
If you haven't already, sign up for the Elm Weekly Newsletter to receive an early access discount coupon in your email!
About the Author
Table of Contents
- Introduction
- About the Author
- Chapter 1: Elm: Delightful Constraints
- React Recommends, Elm Requires and Enables
- When Constraints Give Freedom
- The Debugging Clarity
- Refactoring with Confidence
- The Architectural Discipline
- What This Costs You
- What Elm Teaches You
- Chapter 2: The Elm Architecture – A Recipe for Reliable Apps
- The Recipe: Four Simple Ingredients
- Ingredient 1: Model - Your State Shape
- Ingredient 2: Msg - Things That Can Happen
- Ingredient 3: update - How State Changes
- Ingredient 4: view - Rendering Your State
- Putting It All Together: Counter with Undo
- The Elm Runtime Loop
- What React Developers Already Know
- What Makes TEA Different
- The Price of Explicitness
- What You Just Learned (The FP Hiding in Plain Sight)
- What’s Next
- Chapter 3: Your First Elm App
- Installing Elm
- Editor Setup
- Setting Up Your Project
- The obligatory “Hello, world!”
- Two Flavors of main
- The LGTM Generator: Building It Step by Step
- Building Your First Elm App
- Compiler-Driven Development in Action
- What You Just Built
- Chapter 4: Starting Small: Elm in Your React Codebase
- Widget-by-widget Incremental Adoption Strategy
- Integrating One Elm Component into React
- Build Systems and Toolchain Integration
- Scaling This Approach
- Chapter 5: Commands and Randomness
- Upgrading from Browser.sandbox to Browser.element
- The Cmd Type and How It Works
- Adding Randomness to the LGTM Generator
- What You Just Learned
- Chapter 6: HTTP and Remote Data
- From Random.generate to Http.get
- Setting Up the Server
- Installing elm/http
- The Shape of HTTP in Elm
- Success | Loading | Error
- Creating the HTTP Request
- Updating init
- Refactoring the GotPhrase Message
- Handling Results in update
- Rendering Different States
- The Complete Code
- Commands Are Just Commands
- What You Just Learned
- Chapter 7: JSON Decoders and Type Safety
- Why JSON Needs Decoding in Elm
- Supporting JSON in Our LGTM Generator
- What About Sending JSON?
- What You Just Learned
- Further Reading
- Chapter 8: JavaScript Interop: Ports and Flags
- JavaScript as Infrastructure
- Upgrading Our Build for Manual Bootstrapping
- Flags as Program Input
- Ports for Communicating with JavaScript
- Adding Clipboard Support to the LGTM Generator
- What You Just Learned
- What’s Coming
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