The Origin of Stimulus
This is the way of the majestic monolith. Basecamp runs across half a dozen platforms, including native mobile apps, with a single set of controllers, views, and models created using Ruby on Rails. Having a single, shared interface that can be updated in a single place is key to being able to perform with a small team, despite the many platforms.
That’s not to say that there isn’t value in such an approach for some people, some of the time. Just that as a general approach to many applications, and certainly the likes of Basecamp, it’s a regression in overall simplicity and productivity.
We wanted Basecamp to feel like that too. As though we had followed the herd and rewritten everything with client-side rendering or gone full-native on mobile.
This desire led us to a two-punch solution: Turbo and Stimulus.
﹟Turbo up high, Stimulus down low
To get around this reinitialization, Turbo maintains a persistent process, just like single-page applications do. But largely an invisible one. It intercepts links and loads new pages via Ajax. The server still returns fully-formed HTML documents.
This strategy alone can make most actions in most applications feel really fast (if they’re able to return server responses in 100-200ms, which is eminently possible with caching). For Basecamp, it sped up the page-to-page transition by ~3x. It gives the application that feel of responsiveness and fluidity that was a massive part of the appeal for single-page applications.
But Turbo alone is only half the story. The coarsely grained one. Below the grade of a full page change lies all the fine-grained fidelity within a single page. The behavior that shows and hides elements, copies content to a clipboard, adds a new todo to a list, and all the other interactions we associate with a modern web application.
While it was easy to add new code like this, it wasn’t a comprehensive solution, and we had too many in-house styles and patterns coexisting. That made it hard to reuse code, and it made it hard for new developers to learn a consistent approach.
﹟The three core concepts in Stimulus
Stimulus rolls up the best of those patterns into a modest, small framework revolving around just three main concepts: Controllers, actions, and targets.
It’s designed to read as a progressive enhancement when you look at the HTML it’s addressing. Such that you can look at a single template and know which behavior is acting upon it. Here’s an example:
<div data-controller="clipboard"> PIN: <input data-clipboard-target="source" type="text" value="1234" readonly> <button data-action="clipboard#copy">Copy to Clipboard</button> </div>
As you can see, Stimulus doesn’t bother itself with creating the HTML. Rather, it attaches itself to an existing HTML document. The HTML is, in the majority of cases, rendered on the server either on the page load (first hit or via Turbo) or via an Ajax request that changes the DOM.
Stimulus is concerned with manipulating this existing HTML document. Sometimes that means adding a CSS class that hides an element or animates it or highlights it. Sometimes it means rearranging elements in groupings. Sometimes it means manipulating the content of an element, like when we transform UTC times that can be cached into local times that can be displayed.
There are cases where you’d want Stimulus to create new DOM elements, and you’re definitely free to do that. We might even add some sugar to make it easier in the future. But it’s the minority use case. The focus is on manipulating, not creating elements.
If, on the other hand, you have nagging sense that what you’re working on does not warrant the intense complexity and application separation such contemporary techniques imply, then you’re likely to find refuge in our approach.
﹟Stimulus and related ideas were extracted from the wild
At Basecamp we’ve used this architecture across several different versions of Basecamp and other applications for years. GitHub has used a similar approach to great effect. This is not only a valid alternative to the mainstream understanding of what a “modern” web application looks like, it’s an incredibly compelling one.
In fact, it feels like the same kind of secret sauce we had at Basecamp when we developed Ruby on Rails. The sense that contemporary mainstream approaches are needlessly convoluted, and that we can do more, faster, with far less.
Furthermore, you don’t even have to choose. Stimulus and Turbo work great in conjunction with other, heavier approaches. If 80% of your application does not warrant the big rig, consider using our two-pack punch for that. Then roll out the heavy machinery for the part of your application that can really benefit from it.
At Basecamp, we have and do use several heavier-duty approaches when the occasion calls for it. Our calendars tend to use client-side rendering. Our text editor is Trix, a fully formed text processor that wouldn’t make sense as a set of Stimulus controllers.
This set of alternative frameworks is about avoiding the heavy lifting as much as possible. To stay within the request-response paradigm for all the many, many interactions that work well with that simple model. Then reaching for the expensive tooling when there’s a call for peak fidelity.
Above all, it’s a toolkit for small teams who want to compete on fidelity and reach with much larger teams using more laborious, mainstream approaches.
Give it a go.
David Heinemeier Hansson