Svelte. On rails! Awesome.

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 rollup.

Server-side rendering is the bottleneck on such a pipeline.
Although rollup is powerful, this gem is in an early state
and there may be limitations.

Javascript is written in ESM syntax, orientated by the functionality of vite.
Although the common-js plugin is installed, I have not tested it,
so for example require may not work in Svelte components.

But we have done everything we can to make your setup work smoothly.

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

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 path do

bundle add svelte-on-rails

and run the fat installer

rails svelte_on_rails:install_haml_vite

this installer guides you through and if you answer all with yes,
at the end, you just have to (re-) start your server
and you will see a Svelte component!

Minimal Installation

within the app folder

bundle add svelte-on-rails

rails svelte_on_rails:install

This will create a little config file, installs the npm package,
creates a initializer file and adds the import statement on appplication.js entrypoint file

Minimal installer

There is also a minimal installer:

rails 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';

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

rails svelte_on_rails:toggle_hello_world_svg

toggles the svg nested to the hello world component for check if thee svg is refreshed when imported image changes

rails svelte_on_rails:reset_and_compile_all

This does the same step that ist triggered together with the
rails assets:precompile step together with the deployment pipeline:
it removes all contents of the svelte-on-rails compiled
assets and compiles them all new.

Performance

Example from the rails console for a medium complex component

  • Compiled MyComponent.svelte.js: 0.411ms
    • => happens only once
  • Rendered MyComponent.svelte server-side: 0.518ms
    • => happens on every SSR request
  • Rendered MyComponent.svelte as empty element that will be mounted on the client side
    • => subsequent calls
  • Completed 200 OK in 521ms (Views: 520.2ms | ActiveRecord: 0.0ms (0 queries, 0 cached) | GC: 0.3ms)

Testing

Testings are within the gem by rspec. And there is a rails project with
testings (based on playwright) where the npm package and this gem is tested together.

Licence

License is MIT