A Simple Guide to GatsbyJS Themes

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Kyle Gill, Senior Software Engineer, Gatsby

Last updated

(Gatsby v2.3.25)

Gatsby recently announced themes, and I got excited. Upon reading through all sorts of write-up on them, my response at first was “huh?” A lot of cool technical speak sounded impressive, but until I started tinkering around with them it was hard to see just how exciting they could be.

Since digging into them I now am of the opinion that with themes, what’s already powerful about Gatsby turns into an even more heavily customizable juggernaut of a tool. This post looks at the advantages of themes from a more beginner, higher-level approach, as well as how a theme can be implemented in a Gatsby site (not how themes are authored, which other resources cover).

Understanding Themes

A Gatsby theme is installed as an npm package, but at its core is setup like any other Gatsby site. Essentially, you can convert one Gatsby project into a reusable building block for other Gatsby projects. This flexibility means you can utilize a theme for multiple sites with use cases like:

  • Abstracting away configurations setting up Gatsby plugins like gatsby-mdx or gatsby-image
  • Sourcing data from multiple locations like WordPress, Shopify, or your own microservices
  • Updating shared functionality once and propagating changes with a simple npm install of your theme
  • Making big money cranking out sites for clients faster than the US Economy can go into debt 💰

Thinking of themes as an npm package is useful to understand the power that this abstraction brings to development. Just like package authors of npm can expose more or less of an API to provide greater or less flexibility at different tradeoffs, Gatsby theme authors can provide varying levels of control to users of the theme, providing configuration setup, styling rules, or whole components!

(Think about how much time you’ll save when you eliminate all the time you spend debugging how you broke node-sass again.)

The Possibilites with Themes

In the words of Jason Lengstorf in a podcast interview on JavaScript to Elm:

A theme is effectively a composable Gatsby config

Just like functions in programming can be composed together like little mathematical nesting dolls, multiple themes can be composed together.

A theme can be installed in another Gatsby project to make a parent theme, a child theme, or even be composed together horizontally to use multiple themes in a single site. You’re able to install a blog theme that houses all the details for your blog, a separate e-commerce theme that can support checkout, and then a styling theme that lays a skin over all the rest of them.

Why use Themes?

This exact topic is covered in this blog post by Kyle Mathews. To sum up some of his points and further his argument, themes provide a higher-level approach to working with Gatsby that abstract away the complex or repetitive parts into a reusable package.

A traditional “one-off” Gatsby sites take a broad array of resources and combines them into a site, but each of those resources is handled individually and has to be added one at a time.

Gatsby starters help to reduce that repetition, allowing you to make a boilerplate of each compose-able plugin or setting you wanted. That starter could be cloned right to where you want to start developing, but what happens when you want to update changes to 20 sites you’ve made from the same starter? The starter has basically been “ejected”, its git history deleted, and you’re left making updates across 20 different repositories with slightly adjusted implementation details.

Gatsby sites consume a variety of resources in what is dubbed the “content mesh” Gatsby sites consume a variety of resources in what is dubbed the “content mesh”

Themes solve that headache by allowing entire sites and configurations to be packaged up together. You can convert a site into a theme and then rather than pulling in and installing each plugin or asset you want each time you create a new site, the theme can be pulled in that handles all of those for you.

Imagine having the ability to maintain your docs in a Gatsby site by (1) installing a theme (2) filling a folder with markdown files and (3) deploying, using the configuration setup by a theme author. (If you like that idea, great! Because we’re going to do it together 🙌)

A reusable configuration can be packaged up as a theme and implemented in a new site A reusable configuration can be packaged up as a theme and implemented in a new site

Themes are not stamped out, cookie cutter sites cloned into an entirely new repo like a WordPress theme. They are upstream pieces of your application that are consumed by your Gatsby project (potentially, many Gatsby projects).

How to use Themes

So how do you make themes work? All of this sounds awesome, but so does cooking Baked Alaska, until you realize that the process of cooking involves lighting it on fire.

Using themes in Gatsby is a similar process to using plugins in Gatsby, but I’m going to walk through what’s happening at each step to spell out what’s happening as simple as I can make it.

This tutorial assumes a general understanding the Gatsby, if you’re unfamiliar with what’s going on you can get up to speed here or send me a message 🙂

I’m beginning with the default Gatsby starter, running this command will generate a new Gatsby site and navigate into it:

gatsby new gatsby-site && cd gatsby-site

I can then install a theme into a site much like how a Gatsby plugin would be installed. I’m going to install the gatsby-theme-docz theme, which will do the setup around configuring MDX files and generating docs for me.

Note: MDX is a format that lets you write JSX inside of Markdown files, basically letting us write in markdown as well as including React components alongside it, pretty cool!

yarn add gatsby-theme-docz

Then I’ll open up my gatsby-config.js file to and include the name of the theme I’m using in the plugins array:

// gatsby-config.js
module.exports = {
siteMetadata: {
plugins: ["gatsby-theme-docz"],

With that added, my project now relies on what I’ve defined in my config as well as what is defined in the theme’s config. Now I can start using any of the setup that the theme supplies in my project (in this case, MDX). Adding a new .mdx file to the src/pages directory is enough to let the theme do the heavy lifting of configuring exactly how gatsby-mdx will behave (without me worrying about it).

I added a file called image.mdx that I’ll use to show off gatsby-image which comes installed with the Gatsby default starter (and gives me speedy, optimized images without any of the pain). Then inside of the file I added, some really simple markdown and JSX:

// src/pages/image.mdx
import Img from '../components/image.js'
# Image Component Example
Using the Gatsby image component makes performance fun again:
<Img />

This file shows how powerful MDX can make authoring by allowing components to be imported right into markdown and then included right next to our plain markdown. We’re importing the Image component (that is already a part of the default starter) and using it like it would be written in normal React code.

Now start up your server by running gatsby develop from the terminal and navigate to [http://localhost:8000/image](http://localhost:8000) in the browser:

The most comprehensive docs since AWS The most comprehensive docs since AWS

Just like that, I now have the Docz theme:

  • supplying the configuration for Gatsby MDX
  • turning .mdx files in the src/pages directory into new doc examples
  • putting a cool search bar on the left side of created pages for all the MDX files I add (you won’t find that component anywhere in the project, but it is still configurable thanks to component shadowing)

If I decide that there is a component in an imaginary theme gatsby-theme-abc that I want to use in my project I can import it from its path like this:

import UsefulThing from 'gatsby-theme-abc/src/components/Useful'

Components, data, configuration, constants/tokens, they can all be wrapped up and passed down into the project where the theme is being used.

This example is pretty small, but imagine having a whole series of sites leveraging multiple themes that utilize your design system, checkout flow, or data fetching. When they are all just made up of themes, the designers can focus on designing, and theme authors can neatly package up exactly what they want, and the possibilities are awesome.

You can view the code used for this demo here:

I’m really excited about themes and think they are deserving of the hype around them. There have already been a lot of cool uses for them in addition to projects like Docz. For instance, Apollo uses their own custom Gatsby theme for consistent experiences across their docs, and spinning up derivative sites like Principled GraphQL.

More advanced patterns will surely emerge in time and prove just how much can be done with themes.

Thanks for reading!…

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