Latent Component Shadowing

A set of components that aren't used until a specific theme is also installed, at which point they shadow that theme's components

With Gatsby Themes we've been thinking about the different layers that will likely exist in the ecosystem. When I try to boil it down I end up with something like:

Emerging patterns

The Data Model handles the sourcing of data and its transformation to a standard type/schema. In the wild there are pretty standardized object types like BlogPosts and StoreItems so we could expose officially supported models.

Additionally, the templating system is something that's pretty standard as well. Blog posts might be rendered to different pages like /writing or /thoughts in place of /blog but that's a configuration detail. If we also expose a standard set of templating themes we open up a new layer for themes developers that can operate entirely in the React/styling world without touching gatsby-node.js or GraphQL.

Rendering

The rendering layer is where we'll see a lot of exciting innovation since suddenly designers and developers will be able to build powerful Gatsby sites and applications without needing to learn Gatsby's node APIs or GraphQL. This is great because we can now operate at a new layer of abstraction that progressively discloses complexity.

In essence, new themes will be able to be built on top of other themes that leverage Component Shadowing to tap into the rendering of a page and customize it.

Horizontal composition

We anticipate horizontal composition to be a common pattern for combining themes together. When you think about the architecture of websites, they're often grouped based on their data source.

So we can consider a scenario where a theme author wants to build gatsby-theme-tomato which supports a blog, portfolio, and ecommerce store. Then end user of the theme, if using all three sources, would end up with a theme composition looking like the following:

shopify => gatsby-data-ecommerce => gatsby-theme-ecommerce  \
                                                             \
contentful => gatsby-data-blog => gatsby-theme-blog --------- gatsby-theme-tomato
                                                              /
instagram => gatsby-data-portfolio => gatsby-theme-portfolio /

Ideally, gatsby-theme-tomato would be able to build React components that interfaced with the themes above and not need to know about how they source data or even render the templates. With Component Shadowing, this is possible!

Gatsby Theme Tomato

If we know the architecture of a theme that we'll support we can now create a "bag of components" that are built around Latent Component Shadowing. This allows the gatsby-theme-tomato developer to support a collection of built in themes that are automatically activated when the data source and template are "turned on" when a theme like gatsby-theme-blog is installed and configured.

├── gatsby-theme-tomato
   ├── gatsby-config.js
   ├── gatsby-node.js
   ├── package.json
   └── src
       ├── components
       │   ├── header.js
       │   ├── footer.js
       │   ├── layout.js
       │   ├── ...
       ├── gatsby-theme-blog
       │   └── components
       │       ├── post.js
       │       └── posts.js
       ├── gatsby-theme-store
       │   └── components
       │       └── store.js
       ├── gatsby-theme-portfolio
           ├── portfolio.js
           └── portfolio-item.js

If a user starts with the following config:

// gatsby-config.js
module.exports = {
  __experimentalThemes: ['gatsby-theme-blog', 'gatsby-theme-tomato']
}

All the blog posts will be rendered by gatsby-theme-tomato because the theme is shadowing the Post and Posts components which are being rendered by the templates in gatsby-theme-blog.

Then, down the road a user might decide they want to add a portfolio:

// gatsby-config.js
module.exports = {
  __experimentalThemes: [
    'gatsby-theme-blog',
    'gatsby-theme-portfolio',
    'gatsby-theme-tomato'
  ]
}

When gatsby develop is restarted, gatsby-theme-tomato takes over the rendering of the portfolio theme as well.

This is leveraging Latent Component Shadowing.

A real world application

I'm currently working on a project called Digital Garden that is using Latent Component Shadowing.

The idea is that gatsby-theme-digital-garden is the base. It sources your notes directory and creates pages for each note and a directory listing. This is the default behavior and is meant to be mixed in with any existing Gatsby site.

However, I want to be able to add in additional functionality to the ecosystem if you're starting with the base. So, for my own site I wanted blog functionality as well. So I've added gatsby-theme-digital-garden-blog which is intended to be a sibling of gatsby-theme-digital-garden. All components and styling thus live in the base theme and lay dormant until gatsby-theme-digital-garden-blog activates.

├── gatsby-theme-digital-garden
│   └── src
│       ├── components
│       │   ├── directory-list.js
│       │   ├── file-list.js
│       │   ├── header.js
│       │   ├── layout.js
│       │   ├── note.js
│       │   ├── notes.js
│       │   └── ui.js
│       ├── gatsby-theme-digital-garden-blog
│       │   └── components
│       │       ├── header.js
│       │       ├── layout.js
│       │       ├── post.js
│       │       └── posts.js
│       ├── templates
│       │   ├── note.js
│       │   └── notes.js
└── gatsby-theme-digital-garden-blog
    └── src
        └── templates
            ├── post.js
            └── posts.js

It's an interesting approach because the rendering of any theme in the Digital Garden ecosystem is supported in the base theme and the templating for some functionality like the blog or portfolio needs to be installed and added to the Gatsby config:

// gatsby-config.js
module.exports = {
  __experimentalThemes: [
    'gatsby-theme-digital-garden',
    'gatsby-theme-digital-garden-blog'
  ]
}

Why should the base theme handle rendering?

In the context of Digital Garden, I want a single design token configuration to automatically apply to all components. Down the road we'll also add functionality like light/dark mode and other ways to customize layouts and other aspects.

Due to these needs it makes sense for all the components to be colocated. You could also break out these components to a standalone npm library that's shared amongst all Digital Garden themes, but these components will only ever be used as a Gatsby theme so there isn't a need.

Conclusion

Latent Component Shadowing can be a powerful way as a theme author to add support for a collection of themes that handle data sourcing, page creation, and templating. You can operate solely at the React level and build new things without needing to dive into the lower levels of Gatsby until you need to. You simply write components that lay dormant until they're activated by a sibling theme.

Thanks to @jxnblk for coining the term. My working name was "predictive shadowing" and knew a better word was eluding me.

Thanks to @jlengstorf and @chrisbiscardi for nerding out with me a bunch on this topic.