This repository is an example Laminar Scala.js application complete with a Vite dev server, http4s backend, docker deployment of production builds, and many other features. It mainly focuses on the following aspects:
- Laminar examples
- Scala.js <> JS interop patterns
- Scala.js <> JVM interop patterns
- Build config for dev & prod + packaging
More details below.
It's hosted on Fly.io for free, so the server may take a few seconds to boot up if it hasn't been used recently.
The development of learning materials like this is made possible by Laminar sponsors.
HeartAI is a data and analytics platform for digital health and clinical care.
Aurinko is an API platform for workplace addons and integrations.
- Development Setup
- Production Setup
- How To Use This Repo
- Features
- Documentation
- Not Included
- Wishlist
To run this project, you will need to have installed:
- node.js (latest LTS, e.g. v20)
- JDK (latest LTS, e.g. v17)
- sbt (latest 1.x)
Note: There are essentially two versions of sbt: the version used in the project, and the version of the sbt script that you've installed back in the day when you first started using sbt on your computer. The project sbt version defined in our build.properties file, but the script sbt version does not get auto-updated, so it could be very old. If it's 0.13.x, you can face weird build errors. Check using sbt --version, and go install the latest sbt 1.x if you see script version 0.13.x.
Note: you don't need to install Scala yourself: sbt manages all Scala dependencies according to our build.sbt file, including the Scala compiler itself.
The first time only, to install JS dependencies, run this in your terminal:
cd client
npm ci
Then, open another terminal window, and run there:
sbt
~client/fastLinkJS
Then, back in the first terminal, run:
npm run dev
All of the above commands will install your JS and Scala dependencies, and start the Vite dev server (npm run dev) along with incremental Scala compilation of your frontend (~client/fastLinkJS). At this point, you can already open the app at
localhost:3000/, and everything that doesn't need a backend will work, which in our case, are most pages.
The wind gradient pages, on the other hand, demonstrate interop with the backend, so to view them, you need to start the http4s server.
Open yet another terminal window, and do this:
sbt
~server/reStart
Now you have Vite dev server serving your frontend and hot-reloading your frontend assets, and sbt-revolver hot-reloading your server when you make changes to your code.
Once you're familiar with this setup, feel free to use sbt shorthand command aliases that I defined in the build.sbt file: cup for ~client/fastLinkJS, and sup for ~server/reStart. Save your fingers / wrists.
In production, there is no Vite dev server, so to test your site in an environment that matches real life more closely, yet without needing to package it into a jar or deploy it to Docker, you can run buildClient in sbt, and start the server with ~server/reStart. Your site will start on localhost:9000 with frontend assets built for production, without any Vite stuff like hot reload on the frontend. This workflow is too slow for frontend development, generally you should use Vite dev server, and only call buildClient when you need a sanity check for a particular issue or a Vite config change, or before deploying.
You can package the whole application into a fat jar with
sbt packageApplication
Then you can run it with java -jar dist/app.jar then go to localhost:9000.
You can also build a Docker image for the app with (note that the tag name does not matter)
docker build --tag laminar-demo .
Then run it with
docker run --rm -p 9000:8080 laminar-demo
and then go to localhost:9000. Of course, you'll need to install and launch Docker for all docker commands.
(First, you need to package the application into a fat jar, as explained above, using sbt packageApplication.)
The project contains a fly.toml file originally generated via the fly launch command.
You can apply it to your account via fly deploy --ha=false and then see that it's live with fly open. (If not logged in already, you need to authenticate with fly auth login.)
You need to have flyctl installed for this to work.
You can see more complete instructions here.
This demo app is actually deployed on a free Fly.io container (laminar-demo.fly.dev), and I also set up a custom domain using these instructions, so that it's available on demo.laminar.dev.
Install it and run it locally in dev mode as shown above. Then, explore the source code. I left a lot of prose comments explaining some of the patterns that I've used, and I was trying to use a variety of patterns just to show them off.
Make sure you're using a good IDE that 1) lets you go-to-definition on every term and type that you see, and 2) gives actually correct autocomplete suggestions. My preference so far is IntelliJ, despite its incomplete Scala 3 support, but VS Code with Metals is another popular alternative. If you don't have go-to-definition, and you don't have autocomplete that shows you which props and methods are actually available in a given context, your Scala development experience will be, frankly, subpar, because all the Scala APIs that you use will appear like puzzling black boxes that require you to obtain answers somewhere else, whereas many answers are available straight in their code.
Laminar examples
- TodoMVC example
- Chart.js example
- Integration with Web Components (SAP UI5 and Shoelace)
- Network requests to JSON API
- Waypoint clientside URL routing
- Styling with scoped CSS using LESS
- Manually crafted facades for JS libraries (chart.js)
- Importing JS Web Components (SAP UI5, Shoelace)
- Including arbitrary JS files and CSS resources
- Cross-build multi-project sbt setup (client + server + shared)
- Shared data models
- JSON serialization using Borer JSON library
- Backend support for clientside Waypoint URL routing
- sbt-buildinfo to get compile-time data from sbt to scala.js
Vite setup
- Special Scala.js vite plugins to work with per-component CSS / LESS files
- Import JS / CSS / LESS file assets for their side effects without Vite warnings
- Import files from relative paths (or an approximation of that)
- Minification and code transformations preserving source maps
- To view source maps, run
npm run build, thennpm run sourcemap-report. You must installsource-map-explorerglobally first:npm i -g source-map-explorer.
- To view source maps, run
- Proxying api calls to your backend
- Static assets like svg icons, static files like robots.txt and favicon
- Hot reload for Scala.js and LESS / CSS
- http4s serving SPA routes, API routes, static assets, and a 404 fallback route
- Fetching and parsing XML weather data from Environment Canada API
- Generating complex Scala.js code with compile-time data
- Passing simple compile-time data to Scala.js using sbt-buildinfo
- Hot server reload using sbt-revolver
- Packaging frontend & backend assets & code in a far jar using sbt-assembly
- Deploying the fat jar in a docker container (e.g. on fly.io)
First, read Approaches to CSS section of Laminar docs. Now, with that in mind, let me explain the styling pattern I'm using in this project.
In this repo, I apply some styles inline with Laminar methods, e.g. listStyles in HomePageView.scala, and some of the styling is coming from Web Components (on UI5 and Shoelace pages), JS libraries (Chart.js charts) or external stylesheets (TodoMVC standard stylesheet).
The bulk of the styling however is coming from my .less files. These are processed by LESS into CSS. The syntax is very much like regular CSS, but with several quality-of-life improvements.
I have one style.less file which contains styles of general applicability, for example I'm resetting margins for some title elements, setting a better default line height, etc.
In the same style.less file I also define several utility CSS classes, and to distinguish them, I prefix their names with u-, for example I can apply u-error to any element displaying an error to make it red.
Then, I have one .scala file and one .less file per component. For example, I have a FormStateView component in FormStateView.scala, and also FormStateView.less stylesheet for that component and its child elements. I assume that you understand nesting in LESS, and how the > CSS child combinator makes the nesting declarations even more restrictive, reducing the leakage of this component's CSS declarations to child components that didn't ask for them.
In .less files, I distinguish components from other elements by giving them TitleCased class names. Components, for styling purposes, are standalone, self-contained elements. They aren't necessarily top-level elements in the DOM tree, for example Tabs is a component that is nested several layers deep inside other components.
Aside from components, there are also, simply, various child elements, that don't form a component on their own. For example, an -inputRow element in FormStateView – it does not stand on its own, it is an implementation detail of the FormStateView. Think of it as a "private method", even though nothing in CSS is private (Web Components notwithstanding).
The difference between Components and these internal elements is thus: each Component gets its own .less file, named after it. The internals of this component are not to be styled anywhere except this file, and any style definitions inside this file must be scoped appropriately to only affect this component, not its children, and not its siblings or parents. The styles for any internal elements like -inputRow must only be defined in the file of the component of which they are part of.
Parent components must not try to override their child components' internals, they can only set "positioning" / "layout" styles on the child components themselves, for example, like we do in WeatherGradientView.less.
Generally, if the parent component needs to modify the style of the child one, it should inform the child of that need by adding an x-<variant> CSS class to it, for example, we could add an x-compact class to the Tabs component, but crucially, we put the style declarations that respond to this class inside the component being styled, i.e. in Tabs.less, not in the parent component.
We use this x-<variant> naming convention whenever we want to change how something renders – think x-selected, x-large, etc. The same applies to internal elements, e.g. we add an x-hasError class to -inputRow elements in FormStateView when it has an error, and needs different coloring.
Lastly, as the .less files mirror the .scala component files, similar patterns are to be observed there, for example the component's scala file should be responsible for creating all of its internal elements like -inputRow.
You can develop this pattern further as you wish. This baseline gives us:
- Modular CSS / LESS files that can be loaded on-demand (using our vite plugins), conveniently co-located near the component's
.scalafiles - Reduced leakage of CSS rules from parent components to child components
- Easy to read component
.lessfiles with clear structure and limited scope
This isn't the one true CSS pattern, it's simply what I prefer myself, and I think is a good start for people who are new to frontend and CSS.
If my explanation / demonstration of this CSS styling pattern isn't very clear, please let me know.
This project is written in Scala 3, but all the libraries that we use work with Scala 2.13 just as well, except the Borer JSON library – for Scala 2 you will need a slightly older version of that one. Alternatively, you could use a different JSON library like uPickle.
We use Scala 3 features relatively sparingly in this project. We use regular braced syntax. If you want to convert this project to Scala 2, you will need to do a few things:
- Add
newto class instantiations that don't have them (thenewkeyword is optional in Scala 3) - Replace extension methods with implicit value classes
- Replace
given-s withimplicit val-s ordef-s - Replace Scala 3 union types in JS interfaces with Scala.js specific alternative:
scala.scalajs.js.|, and theA | Unittypes specifically should be replaced withscala.scalajs.js.UndefOr[A]. - For web components, use the
ofmethod instead ofapply, as explained here. - Instead of exports in Shoelace web components, use boilerplate or inheritance
- Etc.
If you want to contribute a PR with Scala 2 support for this project, I am happy to host it in a scala2 branch, however I will not be maintaining that branch going forward (but, even if outdated, it might still be useful to some people, thus the invitation).
The idea of ScalablyTyped is appealing – it generates Scala type definitions for JS libs from their Typescript types. However, in practice I found that these generated types can be hard to grasp.
I prefer to manually create facades for JS libraries that I use. This is usually very easy – you read the library's docs, and create the types from the information therein, only covering the types and methods that you actually need or care about. You can always add more types later. And you can always make the types more precise later – sometimes I leave stuff untyped (with js.Dynamic or js.Dictionary or js.Object) because I can't be bothered to create the elaborate types that would be needed to fully and faithfully describe some JS APIs.
I prefer this approach because I will be reading the JS library's docs anyway, and encoding my knowledge in Scala types is only a small, one-time speed bump (once you understand how to do that).
I also prefer this approach because the resulting code – including the imports – looks more similar to the library's native JS code, and so figuring out why something doesn't work is easier (because any help you'll find will be in JS, needing a translation to Scala.js).
If you want to give ScalablyTyped a shot, installing it is pretty easy, but make sure to read everything under Usage so that you understand where you need to import the various types from. To speed things up, you should also configure stIgnore to avoid generating Scala types for JS dependencies that you will not be using from ScalablyTypes (at the very least that's UI5, Shoelace, and bootstrap icons in this repo).
As your first exercise, you can try reimplementing my Chart.js integration using ScalablyTyped. There are old commits in this repo with my attempts if you need a reference, although they're not complete. The official Scala.js tutorial uses ScalablyTyped for Chart.js, although as of this writing, they're using an older version of Chart.js than what I'm using here, and the types have shifted around since then.
This repo focuses on the frontend, and the interop between frontend and backend. In this regard, the various backend frameworks aren't all that different. You should be able to swap out the http4s implementation for something else, just take care to set up the routes and JSON codecs similarly to how we do this with http4s, to maintain compatibility with our frontend.
Some of the old commits in this repo were using Armeria and Javalin, although I can't vouch for the quality of my implementations, since I've never used those frameworks before or since (my implementations weren't complete, either).
This repo focuses on the single page application (SPA) architecture (backend is just an API server, the HTML is all built on the frontend). If you would like to contribute an example of the server returning content in HTML, and loading the client scala.js app from that, talk to me about it on Laminar discord. It would be nice to show how to do this alongside the SPA architecture.
I haven't tested this on Windows. I think it should work, but if you run into any Windows-specific problems, or if any setup instructions don't make sense for Windows, please let me know.
I would like to:
- Expand this demo to include a cookbook of good Laminar patterns
- Showcase more Scala.js patterns, e.g. interop of Datetime types between frontend and backend
- Create integrations for more advanced browser features like Websockets
- Make good quality bindings for Shoelace web components (WIP)
- Etc. etc. etc.
All of that would be very nice, and would help the Laminar & Scala.js ecosystems a lot, I think. I'm not sure when I will ever get to doing all that, but if you want to speed it up, you know what to do! :). This repo itself was possible largely thanks to HeartAI's recent boost in their Laminar sponsorship. Things like that move the needle.
Nikita Gazarov – @raquo
Thanks to Antoine for FlyIOScalaJVMDemo and LaminarSAPUI5Bindings, from which this project borrows bits of code (primarily for the sbt-assembly and docker setup and some web component patterns).
This repo is provided under the MIT license.
The logos and avatars of myself, Laminar, and Laminar sponsors are not covered by the MIT license. No license is granted to you for these assets. However, you may still have "fair use" rights, as stipulated by law.
The rocketship favicon file favicon-32x32.png file was generated from Twitter Twemoji, under CC-BY 4.0 license.
