Adds new Action Options, namely :stop and :prevent (#535)

* Add an event action option for stopping propagation

* Add test case for stopping propagation

... by specifying the event explicitly.

* Add test case for ensuring event propagation without stop option

* Improve test case descriptions

... by using the words "implicit" and "explicit" instead of "default"
and "specified".

* Replace `logPropagationContinued` with `log` and `log2`

* Add an event action option for preventing default

* Add test case for using `:prevent` with explicit event name

* Update `README` about the new action options

* Rename `ExtendedAddEventListenerOptions` to `EventModifiers`

* Use delegated getter method for `eventOptions`

... inside `Binding`.

* Process `.preventDefault` and `.stopPropagation` in separate functions

docs/reference/actions.md

@@ -101,6 +101,13 @@ Action option | DOM event listener option
 `:passive`    | `{ passive: true }`
 `:!passive`   | `{ passive: false }`
 
+On top of that, Stimulus also supports the following action options which are not natively supported by the DOM event listener options:
+
+Custom action option | Description
+-------------------- | -----------
+`:stop`              | calls `.stopPropagation()` on the event before invoking the method
+`:prevent`           | calls `.preventDefault()` on the event before invoking the method
+
 ## Event Objects
 
 An _action method_ is the method in a controller which serves as an action's event listener.

src/core/action.ts

@@ -1,13 +1,14 @@
 import { ActionDescriptor, parseActionDescriptorString, stringifyEventTarget } from "./action_descriptor"
 import { Token } from "../mutation-observers"
 import { camelize } from "./string_helpers"
+import { EventModifiers } from "./event_modifiers"
 
 export class Action {
   readonly element: Element
   readonly index: number
   readonly eventTarget: EventTarget
   readonly eventName: string
-  readonly eventOptions: AddEventListenerOptions
+  readonly eventOptions: EventModifiers
   readonly identifier: string
   readonly methodName: string
 

src/core/action_descriptor.ts

@@ -1,6 +1,8 @@
+import { EventModifiers } from "./event_modifiers"
+
 export interface ActionDescriptor {
   eventTarget: EventTarget
-  eventOptions: AddEventListenerOptions
+  eventOptions: EventModifiers
   eventName: string
   identifier: string
   methodName: string
@@ -29,7 +31,7 @@ function parseEventTarget(eventTargetName: string): EventTarget | undefined {
   }
 }
 
-function parseEventOptions(eventOptions: string): AddEventListenerOptions {
+function parseEventOptions(eventOptions: string): EventModifiers {
   return eventOptions.split(":").reduce((options, token) =>
     Object.assign(options, { [token.replace(/^!/, "")]: !/^!/.test(token) })
   , {})

src/core/binding.ts

@@ -3,6 +3,7 @@ import { ActionEvent } from "./action_event"
 import { Context } from "./context"
 import { Controller } from "./controller"
 import { Scope } from "./scope"
+import { EventModifiers } from "./event_modifiers"
 
 export class Binding {
   readonly context: Context
@@ -21,7 +22,7 @@ export class Binding {
     return this.action.eventTarget
   }
 
-  get eventOptions(): AddEventListenerOptions {
+  get eventOptions(): EventModifiers {
     return this.action.eventOptions
   }
 
@@ -31,6 +32,9 @@ export class Binding {
 
   handleEvent(event: Event) {
     if (this.willBeInvokedByEvent(event)) {
+      this.processStopPropagation(event);
+      this.processPreventDefault(event);
+
       this.invokeWithEvent(event)
     }
   }
@@ -47,6 +51,18 @@ export class Binding {
     throw new Error(`Action "${this.action}" references undefined method "${this.methodName}"`)
   }
 
+  private processStopPropagation(event: Event) {
+    if (this.eventOptions.stop) {
+      event.stopPropagation();
+    }
+  }
+
+  private processPreventDefault(event: Event) {
+    if (this.eventOptions.prevent) {
+      event.preventDefault();
+    }
+  }
+
   private invokeWithEvent(event: Event) {
     const { target, currentTarget } = event
     try {

src/core/event_modifiers.ts

@@ -0,0 +1,4 @@
+export interface EventModifiers extends AddEventListenerOptions {
+  stop?: boolean;
+  prevent?: boolean;
+}

src/tests/modules/core/event_options_tests.ts

@@ -131,10 +131,73 @@ export default class EventOptionsTests extends LogControllerTestCase {
     )
   }
 
+  async "test stop option with implicit event"() {
+    this.elementActionValue = "click->c#log"
+    this.actionValue = "c#log2:stop"
+    await this.nextFrame
+
+    await this.triggerEvent(this.buttonElement, "click")
+
+    this.assertActions(
+      { name: "log2", eventType: "click" }
+    )
+  }
+
+  async "test stop option with explicit event"() {
+    this.elementActionValue = "keydown->c#log"
+    this.actionValue = "keydown->c#log2:stop"
+    await this.nextFrame
+
+    await this.triggerEvent(this.buttonElement, "keydown")
+
+    this.assertActions(
+      { name: "log2", eventType: "keydown" }
+    )
+  }
+
+  async "test event propagation without stop option"() {
+    this.elementActionValue = "click->c#log"
+    this.actionValue = "c#log2"
+    await this.nextFrame
+
+    await this.triggerEvent(this.buttonElement, "click")
+
+    this.assertActions(
+      { name: "log2", eventType: "click" },
+      { name: "log", eventType: "click" }
+    )
+  }
+
+  async "test prevent option with implicit event"() {
+    this.actionValue = "c#log:prevent"
+    await this.nextFrame
+
+    await this.triggerEvent(this.buttonElement, "click")
+
+    this.assertActions(
+      { name: "log", eventType: "click", defaultPrevented: true }
+    )
+  }
+
+  async "test prevent option with explicit event"() {
+    this.actionValue = "keyup->c#log:prevent"
+    await this.nextFrame
+
+    await this.triggerEvent(this.buttonElement, "keyup")
+
+    this.assertActions(
+      { name: "log", eventType: "keyup", defaultPrevented: true }
+    )
+  }
+
   set actionValue(value: string) {
     this.buttonElement.setAttribute("data-action", value)
   }
 
+  set elementActionValue(value: string) {
+    this.element.setAttribute("data-action", value)
+  }
+
   get element() {
     return this.findElement("div")
   }