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blog
Dillon Kearns
Introducing elm-pages 🚀 - a type-centric static site generator
Elm is the perfect fit for a static site generator. Learn about some of the features and philosophy behind elm-pages.
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2019-09-24

After a round of closed beta testing (thank you to Brian and the elm-conf 2019 organizing team!), I'm excited to share a new static site generator for Elm!

Matthew Griffith and I have had a lot of design discussions and sending code snippets back-and-forth to get to the current design. A big thank you to Matthew for the great discussions and, as always, his ability to look at the bigger picture and question basic assumptions to come up with awesome innovations!

What is elm-pages exactly?

Well, this site you're looking at right now is built with elm-pages! For example, the raw content for this post is from content/blog/introducing-elm-pages.md.

elm-pages takes your static content and turns it into a modern, performant, single-page app. You can do anything you can with a regular Elm site, and yet the framework does a lot for you to optimize site performance and minimize tedious work.

I see a lot of "roll your own" Elm static sites out there these days. When you roll your own Elm static site, you often:

  • Manage Strings for each page's content (rather than just having a file for each page)
  • Wire up the routing for each page manually (or with a hand-made script)
  • Add <meta> tags for SEO and to make Twitter/Slack/etc. link shares display the right image and title (or just skip it because it's a pain)

I hope that elm-pages will make people's lives easier (and their load times faster). But elm-pages is for more than just building your blog or portfolio site. There's a movement now called JAMstack (JavaScript, APIs, and Markup) that is solving a broader set of problems with static sites. JAMstack apps do this by pulling in data from external sources, and using modern frontend frameworks to render the content (which then rehydrate into interactive apps). The goal is to move as much work as possible away from the user's browser and into a build step before pushing static files to your CDN host (but without sacrificing functionality). More and more sites are seeing that optimizing performance improves conversion rates and user engagement, and it can also make apps simpler to maintain.

This is just the first release of elm-pages, but I've built a prototype for pulling in external data and am refining the design in preparation for the next release. Once that ships, the use cases elm-pages can handle will expand to things like ecommerce sites, job boards, and sites with content written by non-technical content editors. You can find a very informative FAQ and resources page about these ideas at jamstack.org (plus a more in-depth definition of the term JAMstack).

Comparing elm-pages and elmstatic

elm-pages and elmstatic have a lot of differences. At the core, they have two different goals. elmstatic generates HTML for you that doesn't include an Elm runtime. It uses Elm as a templating engine to do page layouts. It also makes some assumptions about the structure of your page content, separating posts and pages and automatically generating post indexes based on the top-level directories within the posts folder. It's heavily inspired by traditional static site generators like Jekyll.

elm-pages hydrates into a single-page app that includes a full Elm runtime, meaning that you can have whatever client-side interactivity you want. It supports similar use cases to static site generators like Gatsby. elm-pages makes a lot of optimizations by splitting and lazy-loading pages, optimizing image assets, and using service workers for repeat visits. It pre-renders HTML for fast first renders, but because it ships with JavaScript code it is also able to do some performance optimizations to make page changes faster (and without page flashes). So keep in mind that shipping without JavaScript doesn't necessarily mean your site performance suffers! You may have good reasons to want a static site with no JavaScript, but open up a Lighthouse audit and try it out for yourself rather than speculating about performance!

Either framework might be the right fit depending on your goals. I hope this helps illuminate the differences!

How does elm-pages work?

The flow is something like this:

  • Put your static content in your content folder (it could be Markdown, elm-markup, or something else entirely)
  • Register Elm functions that define what to do with the frontmatter (that YAML data at the top of your markup files) and the body of each type of file you want to handle
  • Define your app's configuration in pure Elm (just like a regular Elm Browser.application but with a few extra functions for SEO and site configuration)
  • Run elm-pages build and ship your static files (JS, HTML, etc.) to Netlify, Github Pages, or your CDN of choice!

The result is a blazing fast static site that is optimized both for the first load experience, and also uses some caching strategies to improve site performance for repeat visitors. You can look in your dev tools or run a Lighthouse audit on this page to see some of the performance optimizations elm-pages does for you!

The way you set up an elm-pages app will look familiar if you have some experience with wiring up standard Elm boilerplate:

main : Pages.Platform.Program Model Msg Metadata (List (Element Msg))
main =
  Pages.application
    { init = init
    , view = view
    , update = update
    , subscriptions = subscriptions
    , documents = [ markdownHandler ]
    , head = head
    , manifest = manifest
    , canonicalSiteUrl = "https://elm-pages.com"
    }

You can take a look at the Main.elm file for this site to get a better sense of the bigger picture. I'll do a more in-depth explanation of this setup in a future post. The short version is that

init, update, and subscriptions are as you would expect (but maybe a bit simpler since elm-pages manages things like the URL for you).

documents are where you define how to handle the frontmatter and body of the files in your content folder. And the view function gives you the result from your frontmatter and body, as well as your Model.

head is just a function that passes you the metadata for a given page and lets you define tags to put in the <head> (mostly for SEO).

manifest lets you configure some settings that allow your app to be installed for offline use.

And the end result is that elm-pages gets everything it needs about your site in order to optimize it and turn it into a modern, performant site that will get a great Lighthouse audit score! The goal is to make following best practices for a modern, performant static site one of the following:

  • Built-in
  • Enforced by the Elm compiler
  • Or at the very least the path of least resistence

What makes Elm awesome for building static sites

JAMstack frameworks, like Gatsby, can make powerful optimizations because they are dealing with strong constraints (specifically, content that is known at build time). Elm is the perfect tool for the JAMstack because it can leverage those constraints and turn them into compiler guarantees. Not only can we do more with static guarantees using Elm, but we can get additional guarantees using Elm's type-system and managed side-effects. It's a virtuous cycle that enables a lot of innovation.

Why use elm-pages?

Let's take a look at a few of the features that make elm-pages worthwhile for the users (both the end users, and the team using it to build their site).

Performance

  • Pre-rendered pages for blazing fast first renders and improved SEO
  • Your content is loaded as a single-page app behind the scenes, giving you smooth page changes
  • Split individual page content and lazy load each page
  • Prefetch page content on link hover so page changes are almost instant
  • Image assets are optimized
  • App skeleton is cached with a service worker (with zero configuration) so it's available offline

One of the early beta sites that used elm-pages instantly shaved off over a megabyte for the images on a single page! Optimizations like that need to be built-in and automatic otherwise some things inevitably slip through the cracks.

Type-safety and simplicity

  • The type system guarantees that you use valid images and routes in the right places
  • You can even set up a validation to give build errors if there are any broken links or images in your markdown
  • You can set up validations to define your own custom rules for your domain! (Maximum title length, tag name from a set to avoid multiple tags with different wording, etc.)

Progressive Web Apps

Lighthouse recommends having a Web Manifest file for your app to allow users to install the app to your home screen and have an appropriate icon, app name, etc. Elm pages gives you a type-safe way to define a web manifest for your app:

manifest : Manifest.Config PagesNew.PathKey
manifest =
    { backgroundColor = Just Color.white
    , categories = [ Pages.Manifest.Category.education ]
    , displayMode = Manifest.Standalone
    , orientation = Manifest.Portrait
    , description = "elm-pages - A statically typed site generator."
    , iarcRatingId = Nothing
    , name = "elm-pages docs"
    , themeColor = Just Color.white
    , startUrl = pages.index
    , shortName = Just "elm-pages"
    , sourceIcon = images.icon
    }

Lighthouse will also ding you if you don't have the appropriately sized icons and favicon images. elm-pages guarantees that you will follow these best practices (and gives you the confidence that you haven't made any mistakes). It will automatically generate the recommended set of icons and favicons for you, based on a single source image. And, of course, you get a compile-time guarantee that you are using an image that exists! For example, here's what happens if we try to access an image as logo when the actual file is called icon.

sourceIcon = images.logo

We then get this elm compiler error: Missing image compiler error

elm-pages is just Elm!

elm-pages hydrates into a full-fledged Elm app (the pre-rendered pages are just for faster loads and better SEO). So you can do whatever you need to using Elm and the typed data that elm-pages provides you with. In a future post, I'll explain some of the ways that elm-pages leverages the Elm type system for a better developer experience. There's a lot to explore here, this really just scratches the surface!

SEO

One of the main motivations for building elm-pages was to make SEO easier and less error-prone. Have you ever seen a link shared on Twitter or elsewhere online that just renders like a plain link? No image, no title, no description. As a user, I'm a little afraid to click those links because I don't have any clues about where it will take me. As a user posting those links, it's very anticlimactic to share the blog post that I lovingly wrote only to see a boring link there in my tweet sharing it with the world.

I'll also be digging into the topic of SEO in a future post, showing how elm-pages makes SEO dead simple. For now, you can take a look at the built-in elm-pages SEO module or take a look at how this site uses the SEO module.

Next steps

There are so many possibilities when you pair Elm with static content! I'm excited to explore this area further with the help of the community. Here are some features that are on my radar.

  • Allow users to pass a set of HTTP requests to fetch during the build step (for making CMS or API data available statically in the build)
  • An API to programmatically add pages from metadata (rather than just from files in the content folder)
  • Allow users to configure the caching strategy for service workers (through pure Elm config of course)
  • More SEO features (possibly an API for adding structured data, i.e. JSON-LD, for more interactive and engaging search results)

And of course, responding to your feedback! Please don't hesitate to share your thoughts, on everything from the documentation to the developer experience. I'd love to hear from you!

Getting started with elm-pages

If you'd like to try out elm-pages for yourself, or look at some code, the best place to start is the elm-pages-starter repo. See the site live at elm-pages-starter.netlify.com. Let me know your thoughts on Slack, I'd love to hear from you! Or continue the conversation on Twitter!

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