Re-structure turbo-stream[action=morph] support

This commit re-structures the new support for
`turbo-stream[action="morph"]` elements introduced in [hotwired#1185][].

As an alternative to introduce a new Stream Action, this commit changes
existing actions to be more flexible.

For example, the `<turbo-stream method="morph">` element behaves like a
specialized version of a `<turbo-stream method="replace">`, since it
operates on the target element's `outerHTML` property.

Similarly, the `<turbo-stream method="morph" children-only>` element
behaves like a specialized version of a `<turbo-stream
method="update">`, since it operates on the target element's `innerHTML`
property.

This commit removes the `[action="morph"]` support entirely, and
re-implements it in terms of the `[action="replace"]` and
`[action="update"]` support.

By consolidating concepts, the "scope" of the modifications is more
clearly communicated to callers that are familiar with the underlying
DOM interfaces (`Element.replaceWith` and `Element.innerHTML`) that are
invoked by the conventionally established Replace and Update actions.

This proposal also aims to reinforce the "method" terminology introduced
by the Page Refresh `<meta name="refresh-method" content="morph">`
element.

[hotwired#1185]: hotwired#1185

src/core/streams/actions/morph.js

@@ -1,19 +1,24 @@
 import { Idiomorph } from "idiomorph/dist/idiomorph.esm"
 import { dispatch } from "../../../util"
 
-export default function morph(streamElement) {
-  const morphStyle = streamElement.hasAttribute("children-only") ? "innerHTML" : "outerHTML"
-  streamElement.targetElements.forEach((element) => {
-    Idiomorph.morph(element, streamElement.templateContent, {
-      morphStyle: morphStyle,
-      callbacks: {
-        beforeNodeAdded,
-        beforeNodeMorphed,
-        beforeAttributeUpdated,
-        beforeNodeRemoved,
-        afterNodeMorphed
-      }
-    })
+export function morphElement(target, element) {
+  idiomorph(target, element, { morphStyle: "outerHTML" })
+}
+
+export function morphChildren(target, childElements) {
+  idiomorph(target, childElements, { morphStyle: "innerHTML" })
+}
+
+function idiomorph(target, element, options = {}) {
+  Idiomorph.morph(target, element, {
+    ...options,
+    callbacks: {
+      beforeNodeAdded,
+      beforeNodeMorphed,
+      beforeAttributeUpdated,
+      beforeNodeRemoved,
+      afterNodeMorphed
+    }
   })
 }
 

src/core/streams/stream_actions.js

@@ -1,5 +1,5 @@
 import { session } from "../"
-import morph from "./actions/morph"
+import { morphChildren, morphElement } from "./actions/morph"
 
 export const StreamActions = {
   after() {
@@ -25,21 +25,31 @@ export const StreamActions = {
   },
 
   replace() {
-    this.targetElements.forEach((e) => e.replaceWith(this.templateContent))
+    const method = this.getAttribute("method")
+
+    this.targetElements.forEach((targetElement) => {
+      if (method === "morph") {
+        morphElement(targetElement, this.templateContent)
+      } else {
+        targetElement.replaceWith(this.templateContent)
+      }
+    })
   },
 
   update() {
+    const method = this.getAttribute("method")
+
     this.targetElements.forEach((targetElement) => {
-      targetElement.innerHTML = ""
-      targetElement.append(this.templateContent)
+      if (method === "morph") {
+        morphChildren(targetElement, this.templateContent)
+      } else {
+        targetElement.innerHTML = ""
+        targetElement.append(this.templateContent)
+      }
     })
   },
 
   refresh() {
     session.refresh(this.baseURI, this.requestId)
-  },
-
-  morph() {
-    morph(this)
   }
 }

src/tests/fixtures/stream.html

@@ -39,5 +39,9 @@
     <div id="container">
       <input id="container-element">
     </div>
+
+    <div id="message_1">
+      <div>Morph me</div>
+    </div>
   </body>
 </html>

src/tests/functional/stream_tests.js

@@ -1,9 +1,11 @@
-import { test } from "@playwright/test"
+import { expect, test } from "@playwright/test"
 import { assert } from "chai"
 import {
   hasSelector,
   nextBeat,
   nextEventNamed,
+  nextEventOnTarget,
+  noNextEventOnTarget,
   readEventLogs,
   waitUntilNoSelector,
   waitUntilText
@@ -182,6 +184,48 @@ test("receiving a remove stream message preserves focus blurs the activeElement"
   assert.notOk(await hasSelector(page, ":focus"))
 })
 
+test("dispatches a turbo:before-morph-element & turbo:morph-element for each morph stream action", async ({ page }) => {
+  await page.evaluate(() => {
+    window.Turbo.renderStreamMessage(`
+      <turbo-stream action="replace" method="morph" target="message_1">
+        <template>
+          <div id="message_1">
+            <h1>Morphed</h1>
+          </div>
+        </template>
+      </turbo-stream>
+    `)
+  })
+
+  await nextEventOnTarget(page, "message_1", "turbo:before-morph-element")
+  await nextEventOnTarget(page, "message_1", "turbo:morph-element")
+  await expect(page.locator("#message_1")).toHaveText("Morphed")
+})
+
+test("preventing a turbo:before-morph-element prevents the morph", async ({ page }) => {
+  await page.evaluate(() => {
+    addEventListener("turbo:before-morph-element", (event) => {
+      event.preventDefault()
+    })
+  })
+
+  await page.evaluate(() => {
+    window.Turbo.renderStreamMessage(`
+      <turbo-stream action="replace" method="morph" target="message_1">
+        <template>
+          <div id="message_1">
+            <h1>Morphed</h1>
+          </div>
+        </template>
+      </turbo-stream>
+    `)
+  })
+
+  await nextEventOnTarget(page, "message_1", "turbo:before-morph-element")
+  await noNextEventOnTarget(page, "message_1", "turbo:morph-element")
+  await expect(page.locator("#message_1")).toHaveText("Morph me")
+})
+
 async function getReadyState(page, id) {
   return page.evaluate((id) => {
     const element = document.getElementById(id)

src/tests/unit/stream_element_tests.js

@@ -5,11 +5,12 @@ import { assert } from "@open-wc/testing"
 import { sleep } from "../helpers/page"
 import * as Turbo from "../../index"
 
-function createStreamElement(action, target, templateElement) {
+function createStreamElement(action, target, templateElement, attributes = {}) {
   const element = new StreamElement()
   if (action) element.setAttribute("action", action)
   if (target) element.setAttribute("target", target)
   if (templateElement) element.appendChild(templateElement)
+  Object.entries(attributes).forEach((attribute) => element.setAttribute(...attribute))
   return element
 }
 
@@ -197,9 +198,9 @@ test("test action=refresh discarded when matching request id", async () => {
   assert.ok(document.body.hasAttribute("data-modified"))
 })
 
-test("action=morph", async () => {
+test("action=replace method=morph", async () => {
   const templateElement = createTemplateElement(`<h1 id="hello">Hello Turbo Morphed</h1>`)
-  const element = createStreamElement("morph", "hello", templateElement)
+  const element = createStreamElement("replace", "hello", templateElement, { method: "morph" })
 
   assert.equal(subject.find("div#hello")?.textContent, "Hello Turbo")
 
@@ -210,9 +211,9 @@ test("action=morph", async () => {
   assert.equal(subject.find("h1#hello")?.textContent, "Hello Turbo Morphed")
 })
 
-test("action=morph with text content change", async () => {
+test("action=replace method=morph with text content change", async () => {
   const templateElement = createTemplateElement(`<div id="hello">Hello Turbo Morphed</div>`)
-  const element = createStreamElement("morph", "hello", templateElement)
+  const element = createStreamElement("replace", "hello", templateElement, { method: "morph" })
 
   assert.equal(subject.find("div#hello")?.textContent, "Hello Turbo")
 
@@ -223,9 +224,9 @@ test("action=morph with text content change", async () => {
   assert.equal(subject.find("div#hello")?.textContent, "Hello Turbo Morphed")
 })
 
-test("action=morph children-only", async () => {
+test("action=update method=morph", async () => {
   const templateElement = createTemplateElement(`<h1 id="hello-child-element">Hello Turbo Morphed</h1>`)
-  const element = createStreamElement("morph", "hello", templateElement)
+  const element = createStreamElement("update", "hello", templateElement, { method: "morph" })
   const target = subject.find("div#hello")
   assert.equal(target?.textContent, "Hello Turbo")
   element.setAttribute("children-only", true)