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Webpacker-Svelte makes it easy to use Svelte with Webpacker in your Rails applications.

Gem npm package CircleCI

This is a port of @renchap's excellent webpacker-react.

It supports Webpacker 1.2+.

An example application is available:

For more information, see the blog post.


Your Rails application needs to use Webpacker and have the Svelte integration done. Please refer to their documentation documentation for this:

First, you need to add the webpacker-svelte gem to your Rails app Gemfile:

gem 'webpacker-svelte', "~> 1.0.0"

Once done, run bundle to install the gem.

Then you need to update your package.json file to include the webpacker-svelte NPM module:

npm i webpacker-svelte
# Or
yarn add webpacker-svelte

You are now all set!

Note about versions

Webpacker-Svelte contains two parts: a Javascript module and a Ruby gem. Both of those components respect semantic versioning. When upgrading the gem, you need to upgrade the NPM module to the same minor version. New patch versions can be released for each of the two independently, so it is ok to have the NPM module at version A.X.Y and the gem at version A.X.Z, but you should never have a different A or X.


The first step is to register your root components (those you want to load from your HTML). In your pack file (app/javascript/packs/*.js), import your components as well as webpacker-svelte and register them. Considering you have a component in app/javascript/components/hello.js:

import Hello from "components/hello.svelte";
import WebpackerSvelte from "webpacker-svelte";

WebpackerSvelte.setup({ Hello }); // ES6 shorthand for {Hello: Hello}

With Turbolinks

You have to make sure Turbolinks is loaded before calling WebpackerSvelte.initialize().

For example:

import Hello from "components/hello.svelte";
import WebpackerSvelte from "webpacker-svelte";
import Turbolinks from "turbolinks";


WebpackerSvelte.setup({ Hello });

You may also load turbolinks in regular asset pipeline application.js:

//= require "turbolinks"

In that case, make sure your packs are loaded after application.js

Now you can render Svelte components from your views or your controllers.

Rendering from a view

Use the svelte_component helper. The first argument is your component's name, the second one is the props:

<%= svelte_component('Hello', name: 'Svelte') %>

You can pass a tag argument to render the Svelte component in another tag than the default div. All other arguments will be passed to content_tag:

<%= svelte_component('Hello', { name: 'Svelte' }, tag: :span, class: 'my-custom-component') %>
# This will render <span class="my-custom-component" data-svelte-component="Hello" data-svelte-props="..."></span>

Rendering from a controller

class PageController < ApplicationController
  def main
    render svelte_component: 'Hello', props: { name: 'Svelte' }

You can use the tag_options argument to change the generated HTML, similar to the svelte_component method above:

render svelte_component: 'Hello', props: { name: 'Svelte' }, tag_options: { tag: :span, class: 'my-custom-component' }

You can also pass any of the usual arguments to render in this call: layout, status, content_type, etc.

Note: you need to have Webpack process your code before it is available to the browser, either by manually running ./bin/webpack or having the ./bin/webpack-watcher process running.

Hot Module Replacement

HMR may be working for Svelte3 now, but I haven't tested it. See: sveltejs/svelte-loader#92

HMR allows to reload / add / remove modules live in the browser without reloading the page. This allows any change you make to your Svelte components to be applied as soon as you save, preserving their current state.

Once svelte-loader supports HMR for Svelte 3:

  1. Set up the webpack svelte loader svelte for HMR.

    module.exports = {
      test: /\.svelte$/,
      use: [
          loader: "svelte-loader",
          options: {
            // HMR isn't supported for Svelte3 yet
            hotReload: false
            // Emit css that webpacker can extract into a separate css file in production.
           emitCss: true
  2. Set up webpack-dev-server for HMR. This is easy, just switch hmr: true in your webpacker.yml for development!

  3. you now need to use webpack-dev-server (in place of webpack or webpack-watcher).


To work on this gem locally, may want to clone and setup the example application.

Then you need to change the example app Gemfile to point to your local repository and run bundle afterwards:

gem 'webpacker-svelte', path: '~/code/webpacker-svelte/'

Finally, you need to tell Yarn to use your local copy of the NPM module in this application, using yarn link:

$ cd /path/to/webpacker-svelte/javascript/webpacker_svelte-npm-module/
$ yarn install
$ yarn build # compiles the code from src/ to dist/
$ yarn link
success Registered "webpacker-svelte".
info You can now run `yarn link "webpacker-svelte"` in the projects where you want to use this module and it will be used instead.
$ cd /path/to/contacts/
$ yarn link webpacker-svelte
success Registered "webpacker-svelte".
$ yarn install

After launching ./bin/webpack-watcher and ./bin/rails server in your example app directory, you can now change the Ruby or Javascript code in your local webpacker-svelte repository, and test it immediately using the example app.


If you changed the local javascript package, first ensure it is built (see above).

You'll have to install chromedriver to run the tests:

$ brew install --cask chromedriver
# Or
$ npm install -g chromedriver

To run the test suite:

$ bundle execute rake test

If you change the javascript code, please ensure there are no style errors before committing:

$ cd javascript/webpacker_svelte-npm-module/
$ yarn lint


Bug reports and pull requests are welcome on GitHub at Please feel free to open issues about your needs and features you would like to be added.


All credit to @renchap for webpacker-react, this is just a light re-write of that repo to support Svelte!


Webpacker plugin to integrate Svelte into your Rails application



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