Introduce turbo:{before-,}morph-{element,attribute} events

src/core/drive/morph_renderer.js

@@ -33,7 +33,9 @@ export class MorphRenderer extends Renderer {
       callbacks: {
         beforeNodeAdded: this.#shouldAddElement,
         beforeNodeMorphed: this.#shouldMorphElement,
-        beforeNodeRemoved: this.#shouldRemoveElement
+        beforeAttributeUpdated: this.#shouldUpdateAttribute,
+        beforeNodeRemoved: this.#shouldRemoveElement,
+        afterNodeMorphed: this.#didMorphElement
       }
     })
   }
@@ -44,9 +46,36 @@ export class MorphRenderer extends Renderer {
 
   #shouldMorphElement = (oldNode, newNode) => {
     if (oldNode instanceof HTMLElement) {
-      return !oldNode.hasAttribute("data-turbo-permanent") && (this.isMorphingTurboFrame || !this.#isFrameReloadedWithMorph(oldNode))
-    } else {
-      return true
+      if (!oldNode.hasAttribute("data-turbo-permanent") && (this.isMorphingTurboFrame || !this.#isFrameReloadedWithMorph(oldNode))) {
+        const event = dispatch("turbo:before-morph-element", {
+          cancelable: true,
+          target: oldNode,
+          detail: {
+            newElement: newNode
+          }
+        })
+
+        return !event.defaultPrevented
+      } else {
+        return false
+      }
+    }
+  }
+
+  #shouldUpdateAttribute = (attributeName, target, mutationType) => {
+    const event = dispatch("turbo:before-morph-attribute", { cancelable: true, target, detail: { attributeName, mutationType } })
+
+    return !event.defaultPrevented
+  }
+
+  #didMorphElement = (oldNode, newNode) => {
+    if (newNode instanceof HTMLElement) {
+      dispatch("turbo:morph-element", {
+        target: oldNode,
+        detail: {
+          newElement: newNode
+        }
+      })
     }
   }
 

src/core/view.js

@@ -64,7 +64,7 @@ export class View {
         await this.prepareToRenderSnapshot(renderer)
 
         const renderInterception = new Promise((resolve) => (this.#resolveInterceptionPromise = resolve))
-        const options = { resume: this.#resolveInterceptionPromise, render: this.renderer.renderElement }
+        const options = { resume: this.#resolveInterceptionPromise, render: this.renderer.renderElement, renderMethod: this.renderer.renderMethod }
         const immediateRender = this.delegate.allowsImmediateRender(snapshot, options)
         if (!immediateRender) await renderInterception
 

src/tests/fixtures/page_refresh.html

@@ -9,6 +9,45 @@
     <link rel="icon" href="data:;base64,iVBORw0KGgo=">
     <script src="/dist/turbo.es2017-umd.js" data-turbo-track="reload"></script>
     <script src="/src/tests/fixtures/test.js"></script>
+    <script type="module">
+      import { Application, Controller } from "https://unpkg.com/@hotwired/stimulus/dist/stimulus.js"
+
+      const application = Application.start()
+
+      addEventListener("turbo:morph-element", ({ target }) => {
+        for (const { element, context } of application.controllers) {
+          if (element === target) {
+            context.disconnect()
+            context.connect()
+          }
+        }
+      })
+
+      addEventListener("turbo:before-morph-attribute", (event) => {
+        const { target, detail: { attributeName, mutationType } } = event
+
+        for (const { element, context } of application.controllers) {
+          const pattern = new RegExp(`data-${context.identifier}-\\w+-value`)
+
+          if (element === target) {
+            event.preventDefault()
+          }
+        }
+      })
+
+      application.register("test", class extends Controller {
+        static targets = ["output"]
+        static values = { state: String }
+
+        capture({ target }) {
+          this.stateValue = target.value
+        }
+
+        outputTargetConnected(target) {
+          target.textContent = "connected"
+        }
+      })
+    </script>
 
     <style>
         body {
@@ -42,15 +81,18 @@ <h2>Frame to be preserved</h2>
       </turbo-frame>
     </div>
 
-    <div id="stimulus-controller" data-controller="test">
+    <div id="stimulus-controller" data-controller="test" data-action="input->test#capture">
       <h3>Element with Stimulus controller</h3>
+
+      <div id="test-output" data-test-target="output">reset</div>
+      <input>
     </div>
 
     <p><a id="replace-link" data-turbo-action="replace" href="/src/tests/fixtures/page_refresh.html?param=something">Link with params to refresh the page</a></p>
     <p><a id="link" href="/src/tests/fixtures/one.html">Link to another page</a></p>
 
     <form id="form" action="/__turbo/refresh" method="post" class="redirect">
-      <input type="text" name="text" value="">
+      <input id="form-text" type="text" name="text" value="">
       <input type="hidden" name="path" value="/src/tests/fixtures/page_refresh.html">
       <input type="hidden" name="sleep" value="50">
       <input id="form-submit" type="submit" value="form[method=post]">

src/tests/fixtures/test.js

@@ -84,6 +84,10 @@
   "turbo:frame-render",
   "turbo:frame-missing",
   "turbo:before-frame-morph",
+  "turbo:morph",
+  "turbo:before-morph-element",
+  "turbo:morph-element",
+  "turbo:before-morph-attribute",
   "turbo:reload"
 ])
 

src/tests/functional/page_refresh_tests.js

@@ -14,10 +14,67 @@ test("renders a page refresh with morphing", async ({ page }) => {
   await page.goto("/src/tests/fixtures/page_refresh.html")
 
   await page.click("#form-submit")
+  await nextEventNamed(page, "turbo:before-render", { renderMethod: "morph" })
   await nextEventNamed(page, "turbo:render", { renderMethod: "morph" })
 })
 
-test("renders a page refresh with morphing when the paths are the same but search params are diferent", async ({ page }) => {
+test("dispatches a turbo:before-morph-element and turbo:morph-element event for each morphed element", async ({ page }) => {
+  await page.goto("/src/tests/fixtures/page_refresh.html")
+  await page.fill("#form-text", "Morph me")
+  await page.click("#form-submit")
+
+  await nextEventOnTarget(page, "form-text", "turbo:before-morph-element")
+  await nextEventOnTarget(page, "form-text", "turbo:morph-element")
+})
+
+test("preventing a turbo:before-morph-element prevents the morph", async ({ page }) => {
+  const input = await page.locator("#form-text")
+  const submit = await page.locator("#form-submit")
+
+  await page.goto("/src/tests/fixtures/page_refresh.html")
+  await input.evaluate((input) => input.addEventListener("turbo:before-morph-element", (event) => event.preventDefault()))
+  await input.fill("Morph me")
+  await submit.click()
+
+  await nextEventOnTarget(page, "form-text", "turbo:before-morph-element")
+  await noNextEventOnTarget(page, "form-text", "turbo:morph-element")
+
+  await expect(input).toHaveValue("Morph me")
+})
+
+test("turbo:morph-element Stimulus listeners can handle morphing", async ({ page }) => {
+  await page.goto("/src/tests/fixtures/page_refresh.html")
+
+  await expect(page.locator("#test-output")).toHaveText("connected")
+
+  await page.fill("#form-text", "Ignore me")
+  await page.click("#form-submit")
+
+  await expect(page.locator("#form-text")).toHaveValue("")
+  await expect(page.locator("#test-output")).toHaveText("connected")
+})
+
+test("turbo:before-morph-attribute Stimulus listeners can handle morphing attributes", async ({ page }) => {
+  await page.goto("/src/tests/fixtures/page_refresh.html")
+  const controller = page.locator("#stimulus-controller")
+  const input = controller.locator("input")
+
+  await expect(page.locator("#test-output")).toHaveText("connected")
+
+  await input.fill("controller state")
+  await page.fill("#form-text", "Ignore me")
+  await page.click("#form-submit")
+
+  const { mutationType } = await nextEventOnTarget(page, "stimulus-controller", "turbo:before-morph-attribute", { attributeName: "data-test-state-value" })
+
+  await expect(mutationType).toEqual("update")
+  await expect(controller).toHaveAttribute("data-test-state-value", "controller state")
+  await expect(page.locator("#form-text")).toHaveValue("")
+  await expect(page.locator("#test-output")).toHaveText("connected")
+})
+
+
+test("renders a page refresh with morphing when the paths are the same but search params are different", async ({ page }) => {
   await page.goto("/src/tests/fixtures/page_refresh.html")
 
   await page.click("#replace-link")

src/tests/functional/rendering_tests.js

@@ -28,7 +28,7 @@ test.beforeEach(async ({ page }) => {
 
 test("triggers before-render and render events", async ({ page }) => {
   await page.click("#same-origin-link")
-  const { newBody } = await nextEventNamed(page, "turbo:before-render")
+  const { newBody } = await nextEventNamed(page, "turbo:before-render", { renderMethod: "replace" })
 
   assert.equal(await page.textContent("h1"), "One")