Update the rendered DOMs for custom elements whenever called browser script

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Apply hydration for custom elements whenever calling browser script ([#305](https://github.com/marp-team/marp-core/pull/305))
+
 ## v3.2.0 - 2022-05-21
 
 ### Changed

src/browser.ts

@@ -4,24 +4,43 @@ export { observer }
 
 const marpCoreBrowserScript = Symbol()
 
-export const browser = (target: ParentNode = document): (() => void) => {
+export interface MarpCoreBrowser {
+  /** Clean-up observer for applying polyfills. */
+  (): void
+
+  /** Clean-up observer for applying polyfills. */
+  cleanup: () => void
+
+  /**
+   * Update DOMs to apply custom elements for Marp Core. It should call whenever
+   * rendered DOMs rendered by Marp.
+   *
+   * It has exactly same meaning to call `browser()` with the same arguments
+   * again.
+   */
+  update: () => MarpCoreBrowser
+}
+
+export const browser = (target: ParentNode = document): MarpCoreBrowser => {
   if (typeof window === 'undefined') {
     throw new Error(
       "Marp Core's browser script is valid only in browser context."
     )
   }
 
-  if (target[marpCoreBrowserScript]) return target[marpCoreBrowserScript]
-
-  // ---
+  applyCustomElements(target) // Should call in every update of Marp rendering
 
-  applyCustomElements(target)
+  if (target[marpCoreBrowserScript]) return target[marpCoreBrowserScript]
 
   const cleanupObserver = observer({ target })
-  const cleanup = () => {
+  const cleanupFn = () => {
     cleanupObserver()
     delete target[marpCoreBrowserScript]
   }
+  const cleanup = Object.assign(cleanupFn, {
+    cleanup: cleanupFn,
+    update: () => browser(target),
+  })
 
   Object.defineProperty(target, marpCoreBrowserScript, {
     configurable: true,

test/browser.ts

@@ -14,34 +14,56 @@ beforeEach(() => jest.clearAllMocks())
 afterEach(() => jest.restoreAllMocks())
 
 describe('Browser script', () => {
-  it('executes observers for polyfill and fitting', () => {
+  it('executes polyfill observer and set-up for custom elements', () => {
     const spy = jest.spyOn(window, 'requestAnimationFrame')
 
-    const cleanup = browser()
+    const browserInterface = browser()
     expect(spy).toHaveBeenCalledTimes(1)
     expect(polyfill).toHaveBeenCalledTimes(1)
     expect(applyCustomElements).toHaveBeenCalledTimes(1)
-    expect(browser()).toStrictEqual(cleanup)
+    expect(browser()).toStrictEqual(browserInterface)
+    expect(browserInterface).toStrictEqual(expect.any(Function))
+    expect(browserInterface).toStrictEqual(browserInterface.cleanup)
 
     const rafFunc = spy.mock.calls[0][0]
     rafFunc(performance.now())
 
     expect(spy).toHaveBeenCalledTimes(2)
     expect(polyfill).toHaveBeenCalledTimes(2)
 
-    cleanup()
+    browserInterface.cleanup()
     rafFunc(performance.now())
     expect(spy).toHaveBeenCalledTimes(2) // No more calling function after cleanup
   })
 
   describe('with passed shadow root', () => {
-    it('calls polyfills and fitting observer with specific target', () => {
+    it('calls polyfill observer and custom elements set-up with specific target', () => {
       const root = document.createElement('div').attachShadow({ mode: 'open' })
-      const cleanup = browser(root)
+      const browserInterface = browser(root)
 
       expect(polyfill).toHaveBeenCalledWith({ target: root })
       expect(applyCustomElements).toHaveBeenCalledWith(root)
-      cleanup()
+      browserInterface.cleanup()
+    })
+  })
+
+  describe('#update', () => {
+    it('calls itself again to update custom element DOMs', () => {
+      const browserInterface = browser()
+
+      expect(applyCustomElements).toHaveBeenCalledTimes(1)
+      expect(browserInterface.update()).toStrictEqual(browserInterface)
+      expect(applyCustomElements).toHaveBeenCalledTimes(2)
+      browserInterface.cleanup()
+
+      // For shadow root
+      const root = document.createElement('div').attachShadow({ mode: 'open' })
+      const interfaceShadowRoot = browser(root)
+
+      expect(applyCustomElements).toHaveBeenNthCalledWith(3, root)
+      expect(interfaceShadowRoot.update()).toStrictEqual(interfaceShadowRoot)
+      expect(applyCustomElements).toHaveBeenNthCalledWith(4, root)
+      interfaceShadowRoot.cleanup()
     })
   })
 })