Svelte on Rails

Seamless and robust Svelte in Rails integration.

By default, and when installed together with @hotwired/turbo-rails, it renders
svelte components on first request server side («SSR») and for subsequent
requests it provides a empty tag that will be mounted on the frontend by the associated npm package @csedl/svelte-on-rails on the frontend.

This way svelte works perfectly together with turbo. You will never notice
this unpleasant «blink» on the frontend and it is maximum performance
optimized. SSR compilation is handled by vite.

This all is developed on Rails-7 together with vite_rails.

Thanks to shakacode
and ElMassimo because they all helped me with theyr gems.

If you have issues, please open one and contributors are welcome!

Requirements

  • actual node installed on the server
  • tested on ruby 3.2.2 and rails 7.1
  • vite_rails (the installer will install it by option –full or –vite)
  • svelte v5 (see: how to install svelte on rails/vite)
  • turbo (recommended / how to install turbo on rails)
  • if you use special packages (like pug) that requires commonjs, you may need
  • npm on latest versions

Installation from cero

together with haml, vite, svelte and turbo

If you want to start from a new rails app, follow theese tutorials

rails new my-test-app --skip-javascript

within the app add the gem

bundle add svelte-on-rails

and run the installer

rails g svelte_on_rails:install --full

The --full contains:

  • --vite
    • adds vite_rails gem and running the installer
  • --haml
    • adds the gem and converts existing views
  • svelte_on_rails
    • This is not a option, this is always done: Adds a config file and installs @csedl/svelte-on-rails by npm
  • --turbo
    • installs @hotwired/turbo-rails and adds import statement to application.js
  • --svelte
    • adds or updates svelte
  • --hello-world
    • adds a hello world component

You can also use the options you want instead of using --full.
And there is the option --force that would not ask you whether it should overwrite existing files, for automated processes like testing.

This means, if you want all, except haml, you can run:

rails g svelte_on_rails:install --vite --turbo --svelte --hello-world --force

The installer is written carefully: It does not overwrite a file without asking.
It tells you all what he is doing.

At the end, you just have to (re-) start your server
and you will see a Svelte component.

Then, you can run

rails svelte_on_rails:remove_hello_world

and start coding.

Minimal Installation

For example, within a existing app, add the gem and run the installer without any options

rails g svelte_on_rails:install

that does:

  • creating a config file.
  • installs the npm package

please follow the instructions on @csedl/svelte-on-rails
for setup the workflow

Within the config file, there are mainly two important tags:

  • frontend_folder (relative to Rails.root)
  • components_folder (relative to frontend_folder)

Check if it all works

Add a controller and a view with the helper = svelte_component('HelloWorld', items: ['item1', 'item2']).
On loading you will see

  • Rendered HelloWorld.svelte server-side: 0.075ms

On the rails console and you will see «Greetings from svelte»
on your view with a styled «Increment» button.
Styles you find within the svelte component.
Click this button and see that the component is alive.

On @csedl/svelte-on-rails
are details how the frontend part is working.

Without the npm package installed,
or by passing ssr: true and hydrate: false to the view helper,
you would see the same html, and the styled button,
but the increment button would not work.

I inserted very detailed error messages on rails and on the
npm package, for making sure that thisk setup is working.
So please check the logs on your browser.

Import statements

For check which statements are working and actively tested, please check the
components folder within the gem specs.

Among others there are

  • import svg from '../example.svg?raw'
  • “ (svelte component with typescript syntax)
  • import { someFunction } from '../customJavascript.js';
  • import Child from './Child.svelte';

Precompile assets

Usual vite has a vite.config.ts file, that is used for the client side precompilation.

By running this installer it adds a npm runner so that you can do npm run build:ssr
which does the server side precompilation.

The same job is triggered alongside rails assets:precompile for production environments.

On development, when watch_changes is configured, the precompilation is triggered
after any *.svelte file within the configured components_folder changed.

Option ssr: :auto

ssr: :auto is the default option, as set on config file and can be overridden on the view helper.

Works with hotwired/turbo only

By passing the ssr: :auto option to the view helper,
it checks if the request is an initial request (request header X-Turbo-Request-ID is present):

On Initial-Request, it adds the attribute data-svelte-on-rails-initialize-action="hydrate" and
returns a server side rendered component that will be hydrated on the frontend by the npm package.

Otherwise it adds mount instead of hydrate, and renders a empty element, but provided with the
necessary attributes for the npm package.

More details to this point you can find on the npm package.

This works perfectly with hotwired/turbo because the javascript is only
loaded on very first load to the frontend, then the most work is done
in frontend and the server is relieved, except on initial request.
You will see no unpleasant «blink» on the page.

Styles

For 99% of use cases you can just skip this chapter.

You can simply work with global styles as well as styles within the svelte component.

A server-side rendered svelte component has 2 states:

Before hydration

  • The svelte_component view helper renders the styles contained within the component into a style tag within the component’s wrapper element. This has to be done this way because of Turbo.
  • In very, very rare cases, global styles are not applied in the same way as after hydration.

After hydration

  • Svelte adds a style tag inside the header
  • Svelte renders the component again, which removes the style tag inside the component wrapper.

If you notice a "blink”

For the app to look stable, both states must appear in the same way.
Normally this is the case. But if there are problems,
or you want to see the state before hydration, for development purposes, you can pass
the hydrate: false option to the view helper,
and no hydration will happen for this component.

More rake tasks

This tasks are more for testing/playground purposes

rails svelte_on_rails:add_hello_world

rails svelte_on_rails:remove_hello_world

Contributors Guide

Contributors welcome!

After downloaded the gem, please run the task

rake svelte_on_rails:create_contributor_configs_file

and define a generated_test_app_folder_path (required) for apps, generated for the testings.

For development of the npm package @csedl/svelte-on-rails you can set the
local_npm_package_path (optional) and insert the path to the npm package on your local machine.
This will cause the installer, to install the npm package from a local path instead from the npm registry.

Tests are based on the included templates, like the hello world template and on the installer.

Installer tests starting with completely destroy the rails app within the generated_test_app_path,
generating a new rails app and running the installer and test by playwright if the components are working.

component tests only checking if a rails server is alive, and if not, install and run a rails app.
For this is the testing helper start_rails_server_unless_ping. This step may only be slow on the
first run, then it is fast. And on every repeating the test it always overwrites the components
with the components from the template by the testing helper install_hello_world(
['rails_vite_hello_world'],
app_root: generated_rails_app_root,
force: true,
silent: true
). At the end of the test it leaves the rails server running.

On that way a developer can just edit the templates and run a test and see always the refreshed
content on the browser and on the app within the generated_test_app_path.

NOTE: Theese tests are dependend on your environment, including the running ruby version!
I am working on rvm. If you work on a different environment, some (not many) changes may be necessary.
Thats your part :)

The current test cases including (among others):

create a completely new rails app, running the full installer and check if a hello World component is visible and javascript is working.
run assets:precompile within a rails app and check if the gem does its precompiling too.

Licence

License is MIT