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The Why and When of Choosing Elm

the Visual Edition

January 13, 2017

gain a quick understanding of where Elm fits the picture well and where it poses challenges

For a textual version of this content, see here.

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This is a quick overview of why and when you should consider choosing Elm over JavaScript.

What is Elm?

JS gets more complex, Elm gets simpler

The amount of features, or the “API surface”, of JavaScript grows all the time
Elm’s API surface is much much smaller to begin with, and it’s actually been shrinking the past few releases

(Summary of the table)

Elm does not have this, null/undefined, runtime exceptions or multiple paradigms
Elm does have guarantees of correctness, settled-upon tooling and great ease of refactoring
JavaScript has the opposite

Lean development is continuous refactoring

The features on the previous picture, especially the fickleness of refactoring and lack of guarantees, leads to the fact that JavaScript is in fact poorly suited for lean development
Elm, on the other hand, is a dream to work with when the requirements change and the software needs to be adapted

Learning a completely new language may sound like a huge investment, but:

JavaScript is not a very well defined area of expertise. There’s TypeScript, Flow, React, Vue.js, Angular, plus the build tools
Essentially every a JavaScript project is a unique combination of libraries and design decisions
Take at least 1-2 weeks for new developers to familiarize themselves with
Elm takes about 2 weeks for new developers to get productive with

Elm has incredible upsides

Even a newcomer is not likely to inadvertently mess up a codebase, because the language has such strong guarantees
A superb compiler that tells what the problem in my code is, and often suggests how to fix it
The code is very easy to read, and it always follows the same general pattern

What about the “bus factor”, what if Elm’s development was dropped?

We’d be fine using the current version of Elm for the foreseeable future
The committee behind JavaScript specifications have the “One JavaScript” principle, which basically means “everything that has been introduced to JavaScript, stays in JavaScript”
There is no reason why you’d need the new JavaScript features, and if you want to, you can call that from Elm

Elm is a poor fit for things like

Mostly static pages (e.g. news websites)
Very short projects where you actually want to use ready-made UI components (e.g. MVP admin UIs)
Lots of integration with terrible third-party JavaScript (advertisements in particular)
Sites that need page-by-page visibility in search engines

Elm is great for