Single Page Applications (SPAs) in ClojureScript, while often simple, are not always easy to understand. This example project demonstrates what I think is the best way to build SPAs today.
Usage
Make sure you have yarn and the Clojure CLI tools installed.
At development time, run
scripts/dev
# or to clean all build artifacts
scripts/dev --reset
to start a reloading figwheel server, then open http://localhost:9333/ in your browser.
To build a production build, run
scripts/prod
and open dist/index.html in the browser.
The script applies advanced optimizations by default. You can request a non-minified build using scripts/prod --simple.
Principles
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Simplify tooling
Apply the Unix philosophy: use simple tools based on abstractions that make sense. Everything is held together by duck tape (i.e. Bash scripts)
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Data-driven routing
Navigation is a concern of the M and C of your MVC application, not of the V, so routing should be decoupled from the view layer of your application.
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Single global state
A single global state atom is a simple and clear way to manage state. It makes it obvious where state resides. This project uses a single ratom, but to keep things simple it doesn't introduce a state management a la re-frame.
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Explicit resource management
When the user enters a page, the app needs to perform asynchronous side-effects (often network requests) and acquire resources (set up event listeners, timers, stateful objects). Conversely, resources need to be disposed of when leaving the page. Page resource management should be explicitly tied to navigation events, rather than component lifecycle methods.
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Reloadability
Hot reloading while keeping state is critical for developer productivity.
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Embrace NPM
ClojureScript rocks, but JavaScript reaches - and it has a powerful ecosystem. Because CLJS has great JS interop, prefer state-of-the-art NPM libraries over less powerful ClojureScript alternatives. Instead of CLJS-specific CLJSJS jars, directly tap NPM, the delivery path used by thousands of developers.
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Embrace the Web Platform
Modern JS engines ship with high-quality abstractions like fetch and ES6 promises. Use these over CLJS alternatives.
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Error management
Use Promise rejections to signal errors.
Technical details
Reagent
Reagent is deservedly the most popular React wrapper. With its syntax based on hiccup โ the s-expression syntax that in a dream world HTML would have used from the start โ and the Ratom reloading model, it is simple enough for beginners and flexible enough for experts.
Figwheel Main
Use Figwheel Main as the build tool. It's faster, cleaner and actively developed.
Webpack doublebundle
To require NPM dependencies (including, but not limited to, React components) with great reliability, use Webpack to create an auxiliary bundle and include it in the main build via foreign-libs. For more on the rationale, see this post and the official guide.
Router5
The Router5 library offers a data-centric and framework-agnostic routing system. In addition to being built on clean abstractions, it supports registering on-activate and on-deactivate hooks to trigger side-effects. A common use case is to load data when you enter a page, or to clean up resources when you leave a page. See Past and future of client-side routing by Router5's author, Thomas Roch
Code conventions
The -ui suffix for function is used to indicate that the function is a Reagent component and should be used in [square-brackets].
Every subpage of the app lives in a separate namesapce in the cljs-spa.page hierarchy. It exposes a page-ui entry point, as well as optional on-activate and on-deactivate hooks.
A page is in one of three states: :loading, :loaded or :failed. The page-state-ui wrapper shows a spinner while loading, and a sad smiley when the on-activate promise failed.
The app relies on higher-order components like layout-ui and router-ui to hide complexity and for better composability.
Testing
Tests use the excellent Extra Main facility. With scripts/dev running, visit http://localhost:9333/figwheel-extra-main/tests to see the cljs-test-display test runner.
The tests in this project are included for demonstration purposes and are expected to fail.
Additionally, this project is set up for automatic testing using a headless browser:
scripts/tests
Highlights
Given that we use webpack, any React component can be used easily. As an example, the Home page includes the excellent react-select component. See code.
Troubleshooting
When you run into surprising behavior in the browser, the first thing to try is to restart the dev env using
scripts/dev --reset
which clears local compilation caches.
Links
This repository is inspired by Richard Feldman's elm-spa-example.
Don't forget to check out Figwheel Main.
License
MIT
Author
Paulus Esterhazy [email protected]