Stimulus cheatsheet

Lifecycle callbacks

initialize: once, when the controller is first instantiated
connect: anytime the controller is connected to the DOM
disconnect: anytime the controller is disconnected from the DOM

Action descriptors

The data-action value click->hello#greet is called an action descriptor. This particular descriptor says:

click is the event name
hello is the controller identifier
greet is the name of the method to invoke

Common Events Have a Shorthand Action Notation

Stimulus defines click as the default event for actions on <button> elements. Certain other elements have default events, too. Here’s the full list:

Element > Default event

a > click
button > click
form > submit
input > change
input > type=submit click
select > change
textarea > change

Multiple Actions

If an element has muliple actions you can separate each one with a space click->hello#greet click->hello#save.

The element can even have multiple actions for multiple controllers click->hello#greet click->history#save.

Targets

The data-target value hello.name is called a target descriptor. This particular descriptor says:

hello is the controller identifier
name is the target name

When Stimulus loads your controller class, it looks for target name strings in a static array called targets. For each target name in the array, Stimulus adds three new properties to your controller. Here, our source target name becomes the following properties:

this.sourceTarget evaluates to the first source target in your controller’s scope. If there is no source target, accessing the property throws an error.
this.sourceTargets evaluates to an array of all source targets in the controller’s scope.
this.hasSourceTarget evaluates to true if there is a source target or false if not.

Multiple Targets

If an element is a target for multiple controllers you can separate each one with a space hello.name history.text

Naming Conventions

Component	Convention	Rationale
Controller filenames	snake_case.js	Rails works that way
Identifiers	kebab-case	Sometimes used as part of HTML attribute names; analogous to CSS classes, which are conventionally kebab-case
Action names	camelCase	Map directly to JavaScript controller methods
Target names	camelCase	Map directly to JavaScript controller properties
Data attributes	camelCase + kebab-case	Thin wrapper around the HTMLElement.dataSet API; camelCase names in JS, kebab-case attributes in HTML

Data API

Each Stimulus controller has a this.data object with has(), get(), and set() methods. These methods provide convenient access to data attributes on the controller’s element, scoped by the controller’s identifier.

For example, in our controller above:

this.data.has("index") returns true if the controller’s element has a data-slideshow-index attribute
this.data.get("index") returns the string value of the element’s data-slideshow-index attribute
this.data.set("index", index) sets the element’s data-slideshow-index attribute to the string value of index

If your attribute name consists of more than one word, reference it as camelCase in JavaScript and attribute-case in HTML. For example, you can read the data-slideshow-current-class-name attribute with this.data.get("currentClassName").

HTML API

Controller `data-controller`

e.g. <div data-controller="ControllerName">

e.g. Multiple controllers on the same element: <div data-controller="ControllerName AnotherControllerName">

Target `data-target`

e.g. <input data-target="ControllerName.TargetName">

Action `data-action`

e.g. <button data-action="eventName->ControllerName#methodName">Click me</button>

e.g. Multiple actions on the same element: <button data-action="eventName->ControllerName#methodName anotherEventName->ControllerName#anotherMethodName">Click me</button>

Code snippets

HTML

Example HTML from the Stimulus home page

<div data-controller="hello">
  <input data-target="hello.name" type="text">

  <button data-action="click->hello#greet">
    Greet
  </button>

  <span data-target="hello.output">
  </span>
</div>

ayb/stimulus.md