Islands Architecture (Typescript)

The asset pipeline provides a framework to concatenate and minify or compress JavaScript and CSS assets. It also adds the ability to write these assets in other languages and pre-processors such as Typescript and Sass.

I've used Parcel on several projects and before that Webpack. I've found Parcel to be easier to use and so that is the recommendation for Nails.

Setting up a Volume

If you look at your .devcontainer/docker-compose.yml you'll see a line that is commented out.

#- node_modules:/workspace/crates/asset-pipeline/node_modules # Set target as a volume for performance.

Comment that back in and rebuild your devcontainer. This will setup the node_modules folder as a volume and you will get way better performance during builds. This is due to the fact the node_modules folder has many files and docker tries to sync them with your main file system.

Also in your .devcontainer/Dockerfile uncomment the following line.

#RUN sudo mkdir -p /workspace/crates/asset-pipeline/node_modules && sudo chown $USERNAME:$USERNAME /workspace/crates/asset-pipeline/node_modules


We need the following .gitignore file.


Installing Parcel

To install parcel

$ mkdir crates/asset-pipeline
$ cd crates/asset-pipeline
$ npm install --save-dev parcel

Now create an crates/asset-pipeline/index.ts

import './scss/index.scss'

And also crates/asset-pipeline/scss/index.scss

h1 {
    color: red;

Add a scripts section to your package.json

  "scripts": {
    "start": "parcel watch ./asset-pipeline/index.ts",
    "release": "parcel build ./asset-pipeline/index.ts"

npm run start

And now when you run npm install & npm run start parcel will generate your assets into the dist folder. We should also update our ./.gitignore to exclude the generated files.


Adding Images

Create an empty images folder in crates/asset-pipeline/images then your project should now look something like this.

├── .devcontainer/
   └── ...
└── crates/
         ├── .gitignore
         ├── images/
         │   └── ...
         ├── index.scss
         ├── index.ts
         └── node_modules/
             └── ...
         │  └──
         └── Cargo.toml
         └── ...
├── .gitignore
├── Cargo.toml
└── Cargo.lock

What we have

We now have a pipeline to compile Typescript and SCSS assets and a place to store images.

The islands architecture encourages small, focused chunks of interactivity within server-rendered web pages. The output of islands is progressively enhanced HTML, with more specificity around how the enhancement occurs. Rather than a single application being in control of full-page rendering, there are multiple entry points. The script for these "islands" of interactivity can be delivered with web components, allowing the rest of the page to be just static HTML.

Implementing islands architecture

There are several ways to support the islands architecture for example Stimulus, which I've used on multiple projects.

However all modern browser come with web components built in and as they are pretty simple to use it makes sense to implement client side enhancement using this technology.

Example WebComponent

An example of a very simple component create the following in crates/asset-pipelines/components/hello_world.ts.

//define a class extending HTMLElement
class HelloWorld extends HTMLElement {
    connectedCallback () {
      this.innerHTML = 'Hello, World!'

//register the new custom element
customElements.define( 'hello-world', HelloWorld )

Include the element into your app/src/asset-pipeline/index.ts i.e.

import './scss/index.scss'
import './components/hello_world.ts'

To use the element