Elm in Action
Richard Feldman
  • April 2020
  • ISBN 9781617294044
  • 344 pages
  • printed in black & white

This is the definitive book to learn Elm!

Ubaldo Pescatore, Generali
Elm is more than just a cutting-edge programming language, it’s a chance to upgrade the way you think about building web applications. Once you get comfortable with Elm’s refreshingly different approach to application development, you’ll be working with a clean syntax, dependable libraries, and a delightful compiler that essentially eliminates runtime exceptions. Elm compiles to JavaScript, so your code runs in any browser, and Elm’s best-in-class rendering speed will knock your socks off. Let’s get started!

About the Technology

Simply put, the Elm programming language transforms the way you think about frontend web development.

Elm’s legendary compiler is an incredible assistant, giving you the precise and user-friendly support you need to work efficiently. Elm applications have small bundle sizes that run faster than JavaScript frameworks and are famously easy to maintain as they grow. The catch? Elm isn’t JavaScript, so you’ll have some new skills to learn.

About the book

Elm in Action teaches you the Elm language along with a new approach to coding frontend applications. Chapter by chapter, you’ll create a full-featured photo-browsing app, learning as you go about Elm’s modular architecture, Elm testing, and how to work seamlessly with your favorite JavaScript libraries. You’ll especially appreciate author and Elm core team member Richard Feldman’s unique insights, based on his thousands of hours writing production code in Elm. When you’re done, you’ll have a toolbox of new development skills and a stunning web app for your portfolio.
Table of Contents detailed table of contents

Part 1: Getting Started

1 Welcome to Elm

1.1 How Elm fits in

1.2 Expressions

1.2.1 Using elm repl

1.2.2 Building expressions

1.2.3 Booleans and conditionals

1.3 Functions

1.3.1 Defining functions

1.3.2 Importing functions

1.3.3 Creating scope with let-expressions

1.3.4 Anonymous functions

1.3.5 Operators

1.4 Collections

1.4.1 Lists

1.4.2 Records

1.4.3 Tuples


2 Your first Elm application

2.1 Rendering a page

2.1.1 Describing a page using the Html Module

2.1.2 Building a project

2.2 Handling user input with The Elm Architecture

2.2.1 Representing application state with a model

2.2.2 Handling events with messages and updates


3 Compiler as assistant

3.1 Documenting guarantees with type annotations

3.1.1 Adding optional type annotations

3.1.2 Annotating functions with type variables

3.1.3 Reusing annotations with type aliases

3.1.4 Annotating longer functions

3.2 Using case-expressions and custom types

3.2.1 Using case-expressions

3.2.2 Enumerating possibilities with custom types

3.2.3 Holding data in custom types

3.2.4 Representing flexible messages with custom types

3.3 Generating random numbers with commands

3.3.1 Describing random values with Random.Generator

3.3.2 Introducing commands to The Elm Architecture

3.3.3 Generating random values with Random.generate


Part 2: Production-grade Elm

4 Talking to servers

4.1 Preparing for server-loaded data

4.1.1 Modeling incremental initialization

4.1.2 Resolving data dependencies

4.2 Fetching data from a server

4.2.1 Describing HTTP requests

4.2.2 Sending HTTP requests

4.3 Decoding JSON

4.3.1 Decoding JSON strings into results

4.3.2 Decoding JSON collections

4.3.3 Decoding JSON HTTP responses


5 Talking to JavaScript

5.1 Using custom elements

5.1.1 Importing custom elements

5.1.2 Handling custom events

5.1.3 Responding to slider changes

5.2 Sending data to JavaScript

5.2.1 Creating a command using a port

5.2.2 Receiving data from Elm

5.2.3 Timing DOM updates

5.3 Receiving data from JavaScript

5.3.1 Receiving real-time data from JavaScript via ports

5.3.2 Receiving initialization arguments via flags


6 Testing

6.1 Writing unit tests

6.1.1 Introducing tests

6.1.2 Unit testing a JSON decoder

6.1.3 Narrowing test scope

6.2 Writing fuzz tests

6.2.1 Converting unit tests to fuzz tests

6.2.2 Testing update functions

6.2.3 Creating multiple tests with one function

6.3 Testing views

6.3.1 Testing DOM structure

6.3.2 Fuzzing view tests

6.3.3 Testing user interactions


7 Data modeling

7.1 Storing values by keys in dictionaries

7.1.1 Setting up the page

7.1.2 Storing photos by URL in a dictionary

7.2 Modeling trees by using recursive custom types

7.2.1 Defining trees by using custom types

7.2.2 Recursive messages

7.2.3 Event handlers with recursive messages

7.3 Decoding graphs and trees

7.3.1 Decoding dictionaries

7.3.2 Decoding recursive JSON

7.3.3 Accumulating while decoding


Part 3: Building bigger

8 Single-page applications

8.1 Framing the page

8.1.1 Creating Main.elm

8.1.3 Skipping unnecessary renders with Html.Lazy

8.2 Routing

8.2.1 Handling the initial URL

8.2.2 Parsing URL paths

8.2.3 Handing URL changes

8.3 Delegating pages

8.3.1 Revising module structure

8.3.2 Initializing page states

8.3.3 Delegating page logic



Appendix A: Getting set up

A.1 Installing Node.js and NPM

A.2 Installing command-line tools

A.3 Obtaining the Elm in Action repository

Appendix B: Installing Elm packages

B.1 Direct and indirect dependencies

B.2 Semantic versioning in packages

B.2.1 Semantic versioning enforced

B.2.2 Browsing package documentation

B.3 Example: Installing elm/url

Appendix C: Html.Lazy’s change check

C.1 lazy’s check for strings and numbers

C.2 lazy’s check for everything else

C.3 When memory locations stay the same

C.3.1 Memory locations for collections

C.3.2 Memory locations across updates

C.3.3 Memory locations for functions

C.3.4 Named top-level functions always keep the same memory location

What's inside

  • Scalable design for production web applications
  • Single-page applications in Elm
  • Data modeling in Elm
  • Accessing JavaScript from Elm

About the reader

For web developers with no prior experience in Elm or functional programming.

About the author

Richard Feldman is a software engineer at NoRedInk and a well-known member of the Elm community.

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