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This is an introduction to the JavaScript functionality provided by Stacks.

Including the Stacks JavaScript

Section titled Including the Stacks JavaScript

While Stacks is first and foremost a CSS library, it also provides commonly used functionality for some components via JavaScript. This functionality is optional. If you only need the styling parts of Stack, you’re free to ignore the provided JavaScript. The converse is not true: The JavaScript components work under the assumption that the Stacks CSS is available.

Stacks JavaScript is currently included within various Stack Overflow projects automatically. If you’re working on a Stack Overflow project, chances are it’s already available for you! If not, reach out to us and we’ll work on getting it setup.

To include Stacks JavaScript in other projects, do the following.

  • Include the file dist/js/stacks.min.js in your page. For example, if you use the unpkg CDN, add the tag <script src=""></script> to your HTML. See Using Stacks for more information on Unpkg and installing Stacks via NPM.

The Stacks JavaScript components are provided as Stimulus controllers. Stimulus is a library created by Basecamp.

Stimulus allows you to add functionality to your markup in a way that is similar to how you add styling to your markup: by modifying HTML attributes.

Just as you style components by adding classes to the class attribute, with Stacks JavaScript, you’ll give components optional functionality by adding data-… attributes to the HTML.

The basic functional unit of Stimulus, and of a Stacks JavaScript component, is a controller. Controllers are identified by their name, and all Stacks-provided controller names are prefixed with s-…, just like component CSS classes. You give functionality to an HTML element by setting its data-controller attribute.

<div class="s-magic-widget s-magic-widget__awesome" data-controller="s-magic-widget"></div>

Refer to the documentation of individual components on how to configure a component’s behavior.

Creating your own Stimulus controllers

Section titled Creating your own Stimulus controllers

A side effect of including the Stacks JavaScript in your project is that you also have Stimulus available in your page. This means you can not only use Stacks-provided controllers, but also create your own.

For general information about writing code with Stimulus, refer to the official documentation. That documentation generally assumes that you’re writing ES6 code. In order to make it useful without ES6-to-ES5 transpilation, Stacks provides a helper that allows you to write controllers using old-fashioned JavaScript syntax.

This helper is called Stacks.addController and takes two arguments: The name (“identifier”) of the controller, and an object that is analogous to the ES6 class that you would write for your controller, except that it's a plain JavaScript object. All own enumerable properties of that object will be made available on the controller prototype, with the exception of the targets property, which will be available on the controller constructor itself, i.e. statically.

With that, you can create and register the final Hello World controller example from the official documentation like this:

Stacks.addController("greeter", {
targets: ["name"],

greet: function () {
console.log("Hello, " + +"!");

get name() {
return this.nameTarget.value;

We prefix our JavaScript target classes with .js- so that changing or adding a class name for styling purposes doesn’t inadvertently break our JS. This allows us to style elements with any chain of atomic or component classes from Stacks without breaking any additional JavaScript interactivity.

We also try to avoid IDs for both visual styling and JavaScript targeting. They aren’t reusable, visual styling can’t be overwritten by atomic classes, and, like non-.js- classes, we can’t tell if there is JavaScript interactivity attached at a glance.

<div class="s-card bs-lg js-copy">

var button = document.querySelector('.js-copy');
button.addEventListener('click', function() {

<div class="s-card bs-lg">

var button = document.querySelector('.s-card');
button.addEventListener('click', function() {

.s-card {

<div id="card">

var button = document.querySelector('#card');
button.addEventListener('click', function() {

#card {

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