Proposal: pass isPreview value into the event detail in render events

src/core/frames/frame_controller.ts

@@ -288,7 +288,11 @@ export class FrameController
 
   // View delegate
 
-  allowsImmediateRender({ element: newFrame }: Snapshot<FrameElement>, options: ViewRenderOptions<FrameElement>) {
+  allowsImmediateRender(
+    { element: newFrame }: Snapshot<FrameElement>,
+    _isPreview: boolean,
+    options: ViewRenderOptions<FrameElement>
+  ) {
     const event = dispatch<TurboBeforeFrameRenderEvent>("turbo:before-frame-render", {
       target: this.element,
       detail: { newFrame, ...options },

src/core/session.ts

@@ -26,14 +26,16 @@ import { Preloader, PreloaderDelegate } from "./drive/preloader"
 export type FormMode = "on" | "off" | "optin"
 export type TimingData = unknown
 export type TurboBeforeCacheEvent = CustomEvent
-export type TurboBeforeRenderEvent = CustomEvent<{ newBody: HTMLBodyElement } & PageViewRenderOptions>
+export type TurboBeforeRenderEvent = CustomEvent<
+  { newBody: HTMLBodyElement; isPreview: boolean } & PageViewRenderOptions
+>
 export type TurboBeforeVisitEvent = CustomEvent<{ url: string }>
 export type TurboClickEvent = CustomEvent<{ url: string; originalEvent: MouseEvent }>
 export type TurboFrameLoadEvent = CustomEvent
 export type TurboBeforeFrameRenderEvent = CustomEvent<{ newFrame: FrameElement } & FrameViewRenderOptions>
 export type TurboFrameRenderEvent = CustomEvent<{ fetchResponse: FetchResponse }>
 export type TurboLoadEvent = CustomEvent<{ url: string; timing: TimingData }>
-export type TurboRenderEvent = CustomEvent
+export type TurboRenderEvent = CustomEvent<{ isPreview: boolean }>
 export type TurboVisitEvent = CustomEvent<{ url: string; action: Action }>
 
 export class Session
@@ -276,8 +278,8 @@ export class Session
     }
   }
 
-  allowsImmediateRender({ element }: PageSnapshot, options: PageViewRenderOptions) {
-    const event = this.notifyApplicationBeforeRender(element, options)
+  allowsImmediateRender({ element }: PageSnapshot, isPreview: boolean, options: PageViewRenderOptions) {
+    const event = this.notifyApplicationBeforeRender(element, isPreview, options)
     const {
       defaultPrevented,
       detail: { render },
@@ -290,9 +292,9 @@ export class Session
     return !defaultPrevented
   }
 
-  viewRenderedSnapshot(_snapshot: PageSnapshot, _isPreview: boolean) {
+  viewRenderedSnapshot(_snapshot: PageSnapshot, isPreview: boolean) {
     this.view.lastRenderedLocation = this.history.location
-    this.notifyApplicationAfterRender()
+    this.notifyApplicationAfterRender(isPreview)
   }
 
   preloadOnLoadLinksForView(element: Element) {
@@ -348,15 +350,15 @@ export class Session
     return dispatch<TurboBeforeCacheEvent>("turbo:before-cache")
   }
 
-  notifyApplicationBeforeRender(newBody: HTMLBodyElement, options: PageViewRenderOptions) {
+  notifyApplicationBeforeRender(newBody: HTMLBodyElement, isPreview: boolean, options: PageViewRenderOptions) {
     return dispatch<TurboBeforeRenderEvent>("turbo:before-render", {
-      detail: { newBody, ...options },
+      detail: { newBody, isPreview, ...options },
       cancelable: true,
     })
   }
 
-  notifyApplicationAfterRender() {
-    return dispatch<TurboRenderEvent>("turbo:render")
+  notifyApplicationAfterRender(isPreview: boolean) {
+    return dispatch<TurboRenderEvent>("turbo:render", { detail: { isPreview } })
   }
 
   notifyApplicationAfterPageLoad(timing: TimingData = {}) {

src/core/view.ts

@@ -10,7 +10,7 @@ export interface ViewRenderOptions<E> {
 }
 
 export interface ViewDelegate<E extends Element, S extends Snapshot<E>> {
-  allowsImmediateRender(snapshot: S, options: ViewRenderOptions<E>): boolean
+  allowsImmediateRender(snapshot: S, isPreview: boolean, options: ViewRenderOptions<E>): boolean
   preloadOnLoadLinksForView(element: Element): void
   viewRenderedSnapshot(snapshot: S, isPreview: boolean): void
   viewInvalidated(reason: ReloadReason): void
@@ -91,7 +91,7 @@ export abstract class View<
 
         const renderInterception = new Promise((resolve) => (this.resolveInterceptionPromise = resolve))
         const options = { resume: this.resolveInterceptionPromise, render: this.renderer.renderElement }
-        const immediateRender = this.delegate.allowsImmediateRender(snapshot, options)
+        const immediateRender = this.delegate.allowsImmediateRender(snapshot, isPreview, options)
         if (!immediateRender) await renderInterception
 
         await this.renderSnapshot(renderer)

src/tests/functional/rendering_tests.ts

@@ -36,6 +36,16 @@ test("test triggers before-render and render events", async ({ page }) => {
   assert.equal(await newBody, await page.evaluate(() => document.body.outerHTML))
 })
 
+test("test includes isPreview in render event details", async ({ page }) => {
+  await page.click("#same-origin-link")
+
+  const { isPreview } = await nextEventNamed(page, "turbo:before-render")
+  assert.equal(isPreview, false)
+
+  await nextEventNamed(page, "turbo:render")
+  assert.equal(await isPreview, false)
+})
+
 test("test triggers before-render and render events for error pages", async ({ page }) => {
   await page.click("#nonexistent-link")
   const { newBody } = await nextEventNamed(page, "turbo:before-render")