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Introducing Elm as a frontend contender

Replacing React with Elm as our frontend programming language brings risks, rewards, and lots of developer happiness.

Published by Kim Tore Jensen


In the NAIS feature team, our tasks usually involve writing abstractions for developers. These abstractions usually emerge in the form of API backends, Kubernetes operators or sidecars, command-line tools, and the like. And, rarely, we dawdle in web frontend development, which is largely an unknown domain to us. We don’t mind: React is the de facto framework for frontend application development, at least at NAV. And, to use React, the application must be written in Javascript or Typescript.

Javascript has some really nice features that makes it easy to mess up your application and create bugs. Many articles have been written on this, there is no point writing another one. There are some extensions such as Typescript which addresses some of these issues at the cost of flexibility. But then again, we still have null exceptions. We have the option of ignoring error handling. There are the ambiguous “truthy” or “falsy” equality checks, which can be mitigated by using the triple equality sign. However, one simple slip-up and your application may seem to work fine, until one day it trips over itself and reveals a bug.

The Javascript ecosystem is a huge pain point. Even a small boilerplate React application pulls down hundreds of dependencies by default, which is not only a security concern, but also uses a huge amount of network traffic and hard drive space.

Our team has avoided doing frontend work because of these reasons. But we still need to create some frontends. Fortunately, there is a solution that addresses all of these problems.

A short introduction to Elm

Elm is a pure functional programming language created in 2012 by Evan Czaplicki. Elm compiles to JavaScript and is excellent for websites and web apps. It has a strong emphasis on simplicity and quality tooling. This language has many interesting properties, some of which we’ll have a brief look at.

Type system

First of all, the type system is amazing. It enables you to make impossible states impossible. What does this mean? With Elm’s union types, you can create a data model that simply does not allow for ambiguous state. Consider the following data model:

type alias UserData = { id: Int, name: String }

type User
    = Anonymous
    | Authenticated UserData

Either the user is anonymous, or we have an authenticated user with some associated data. We can have as many associated values as we want. It is impossible to access the ID and name fields of an anonymous user. We can already see that this pattern gives some pretty powerful guarantees.

type Msg
    = GotUserResponse (Result Http.Error UserData)

The message GotUserResponse has Result as associated data. The result type also has associated data, which contains either Ok UserData or Err Http.Error, and only that. Again, it is impossible to access the user data if an error occurs, and vice versa.

userFromResponse: Msg -> User
userFromResponse msg = 
    case msg of
        GotUserResponse (Ok user) ->
            Authenticated user

        GotUserResponse (Err _) ->

The above function takes the above Msg and returns either an authenticated user or an anonymous user. The Msg is guaranteed to hold the object we need to create a User, which in turn must hold that object. Any error ensures that we cannot access any such object. The compiler makes impossible states impossible. This simple yet elegant design choice eliminates many possible bugs. So good!

Check out the following talks by Richard Feldman for an in-depth introduction to Elm types.

Pure functional

Elm is a pure functional language. This means that all data is immutable; it is impossible to modify state once an object has been created. This fact guarantees that all function calls are free of side effects. Any code that needs side effects (such as HTTP requests) must be handled explicitly through a callback system through the Elm runtime, and cannot be called directly from a function.

Compiler driven development

Refactoring an Elm application is quite comfortable. You change your type to match the real-world model, and follow the compiler errors through to the other end. When you’re done, you most probably still have a working application again. It sounds too good, but in our experience we find this to be true most of the time.

Introducing Elm to the team

So far, we established that Elm is arguably the proverbial oasis in the desert of frontend programming. I had already started investigating Elm on my free time, so I was quite motivated to introduce it to our technology stack.

Not everyone on our team shared my opinion, and one of our team’s pillars is that important technical decisions should be made by a quorum. That meant addressing our team’s concerns, evaluating each one, and finally aligning our opinions to form a decision.

Before starting on the concerns, it should be duly noted that one team member was more than happy about the prospect of using Elm at work, and that another team member supported Elm solely on the fact that it’s not Javascript. Yet another member reasoned that we should try it out on the basis that we haven’t tried it out yet, and we’ll likely never know if it’s good for us if we don’t try.

Elm is really not the most popular choice of language. In fact, it’s not even listed in the StackOverflow 2021 developer survey. That supposedly puts this wonderful language below COBOL in popularity. What gives?

Most blog posts and talks I found on the topic reveals that people experienced in Elm usually speaks quite warmly of it. They praise the type system and joy of development, and lament using other languages after befriending Elm.

However, with the release of Elm 0.19 in 2019, some language features that people depended on was removed entirely. This was quite an unpopular decision amongst the community, and battle ensued.

There hasn’t been a release of Elm since 2019. Was this going to be a risk to our project?

Small community and lack of Elm jobs

At NAV, we have plenty of React developers, and a small handful of Elm developers. In the professional world at large, things aren’t a whole lot better. The Norwegian train company Vy uses Elm for large parts of their frontend. Barring that, a quick search on didn’t reveal a single Elm oriented job in Norway. If we adopt Elm, what are the chances of finding competent people should the need arise? What happens to maintainability if our Elm programmers leave the team or quit? Will the rest of us need to either learn a technology they aren’t interested in, or perhaps rewrite the whole thing in React?

After asking around on our internal Slack channels, I found two NAV developers who had been working on an Elm project in one of our development teams. They had been enjoying the fun of working with Elm, easy refactoring, and friendly error messages. However, their stack consisted of many frontend applications, and there was a fair bit of context switching between languages, in addition to some duplicate work in order to support some shared functionality.

That team ultimately had differing opinions on Elm, so the project was abandoned after those two developers were relocated to a different team.

The conclusion from one of those Elm developers was that they would recommend Elm for low-risk projects that would not have many frontend inter-dependencies.

Accessibility and re-use

NAV invested considerable resources in developing Aksel, our in-house collection of tooling and components for frontends. These components implement universal design and include buttons, tables, colors, styles, etc.

These come in the form of React components and are not directly compatible with Elm.

Making a team decision

After thinking about these challenges, I spoke with each team member individually, sharing the information I’d gathered, and listening to their responses. Judging from their mostly positive reactions, I decided to facilitate a group discussion where we could reach a decision. Almost everyone on the team joined the discussion.

All agreed that we should evaluate Elm, on the condition that this would be a time-boxed experiment, using two of our developers during two weeks. Afterwards, we would evaluate our results and thoughts, and if we were happy with the outcome, we could continue working on the project in Elm, ultimately deploying it to production.

The scope of the project was known already because we had implemented it in React earlier. We established the work group and decided to start on the next week. As a work methodology, we chose pair programming, which is useful when learning new languages and concepts. Also, having all members of the work group present means that we can make decisions quickly.


The project we wanted to implement was the frontend for NAIS console. Console is an access control software used to set up external services for our software development teams.

Requirements for the frontend were:

Our goal was to re-implement everything in Elm, attaining feature parity with the already existing React application.


Our backend exposes a GraphQL endpoint. GraphQL is a bit more complex than REST—instead of getting fixed data from multiple endpoints as with REST, GraphQL lets you fetch data from multiple sources in a single query, with strongly typed output using a schema. There is more parsing involved with GraphQL, but the benefits are great.

Fortunately, there is a very nice Elm GraphQL library which makes it easy to work with these endpoints in Elm.

We can generate all the types, queries, and mutations that the API requires. The only thing we need to do is start the API server, and run:

elm-graphql http://localhost:3000/query --base Backend --output src


Elm is compatible with Vite, the next generation frontend tooling. Vite provides a development server with hot module reloading, and facilitates production builds. This provides us with the useful commands npm run dev and npm run build. We can make a change in one of our Elm source files, and the code gets automatically reloaded in the browser, keeping the existing state of the application.

For production builds, we compile the Elm code and bundle it together with our static files in a Docker container based on NGINX. All the compiled Elm code runs directly in the browser, so there is no need for a proxy layer in between. Server side rendering is not needed, as the code is already extremely fast.

In the end, we follow our standard procedures for build and deploy: When we push the code to Github, the build runs automatically and deploys the Docker container to the Kubernetes-based NAIS platform.


Application quality

We are extremely confident that our application will not just crash because we forgot to do a null check. The compiler does not allow us to write code that does not handle error cases. This can be a bit tedious when developing, but pays itself back manifold when the code runs in production. Furthermore, we know that functions cannot have side effects on our state, so even though we didn’t write any tests for this application, we feel confident that it works as expected.

Application speed is blazing fast, and the footprint is quite small.

% npm run build
dist/index.html                  0.54 KiB
dist/assets/index.68a03c7a.css   2.72 KiB / gzip: 1.02 KiB
dist/assets/index.92dff5fa.js    69.62 KiB / gzip: 22.81 KiB

Comparison with React

As we had already implemented this frontend in React earlier, I did a quick side by side comparison of the two versions, focusing on the dependency count and asset sizes—and found the results quite disturbing.

Dependencies Dependency size Compiled code size
React 796 637 MB 618 KB
Elm 111 75 MB 70 KB
Efficiency 717% 849% 882%

For our use case, React is quite bloated in comparison to Elm. These numbers translate to less bugs, less network traffic, less disk usage, and shorter build time. Last, but not least: loading time in the browser decreases, not just due to less network traffic, but also less parsing and evaluation of code.


Working with Elm definitely has its benefits. The type system really makes it easy to accurately model the real-world data and avoid certain kinds of bugs.

Even though none of us had worked in a functional programming language before, we found it easy to get started. The syntax was a bit obscure in the beginning, but quickly became natural. Anecdotally, I’ve worked with Golang professionally for around five years. The simplicity of working with data in Elm really makes me lament how terse Go is. Iteration is not really a thing in Elm, we use map and reduce instead. It is very refreshing not having to write for loops to transform data, and similarly, error checking can usually be done in a single statement instead of having to work through it like some checklist.

We are quite happy with the outcome of our Elm endeavour. Our plan forward is to throw away the old React code for this particular project, and keep our Elm code running in production. When the time comes to revamp our NAIS deploy frontend, we will definitely consider doing it in Elm.

We hope that this blog post will encourage more users to try Elm for their frontend projects, to enjoy the benefits of increased developer satisfaction, smaller assets, and less bugs. Thanks for reading; best regards from the NAIS feature team.