Capture navigationType for the measurement in question

README.md

@@ -191,6 +191,18 @@ export type Metric = {
     // (this can be either a mutation or a load event target, whichever
     // occurred last)
     lastVisibleChange?: HTMLElement | TimestampedMutationRecord;
+
+    // describes how the navigation being measured was initiated
+    navigationType: // Navigation started by clicking a link, entering the URL in the browser's address bar or form submission.
+    | 'navigate'
+      // Navigation is through the browser's reload operation.
+      | 'reload'
+      // Navigation is through the browser's history traversal operation.
+      | 'back_forward'
+      // Navigation is initiated by a prerender hint.
+      | 'prerender'
+      // Navigation was triggered with a script operation, e.g. in a single page application.
+      | 'script';
   };
 };
 ```

src/index.ts

@@ -31,7 +31,7 @@ export const init = (options?: TtvcOptions) => {
   window.addEventListener('pageshow', (event) => {
     // abort if this is the initial pageload
     if (!event.persisted) return;
-    void calculator.start(event.timeStamp);
+    void calculator.start(event.timeStamp, true);
   });
 };
 

src/visuallyCompleteCalculator.ts

@@ -4,6 +4,18 @@ import {requestAllIdleCallback} from './requestAllIdleCallback';
 import {InViewportImageObserver} from './inViewportImageObserver';
 import {Logger} from './util/logger';
 
+export type NavigationType =
+  // Navigation started by clicking a link, entering the URL in the browser's address bar or form submission.
+  | 'navigate'
+  // Navigation is through the browser's reload operation.
+  | 'reload'
+  // Navigation is through the browser's history traversal operation.
+  | 'back_forward'
+  // Navigation is initiated by a prerender hint.
+  | 'prerender'
+  // Navigation was triggered with a script operation, e.g. in a single page application.
+  | 'script';
+
 export type Metric = {
   // time since timeOrigin that the navigation was triggered
   // (this will be 0 for the initial pageload)
@@ -22,6 +34,8 @@ export type Metric = {
 
     // the most recent visual update; this can be either a mutation or a load event target
     lastVisibleChange?: HTMLElement | TimestampedMutationRecord;
+
+    navigationType: NavigationType;
   };
 };
 
@@ -82,7 +96,7 @@ class VisuallyCompleteCalculator {
   }
 
   /** begin measuring a new navigation */
-  async start(start = 0) {
+  async start(start = 0, isBfCacheRestore = false) {
     const navigationIndex = (this.navigationCount += 1);
     this.activeMeasurementIndex = navigationIndex;
     Logger.info('VisuallyCompleteCalculator.start()');
@@ -115,12 +129,22 @@ class VisuallyCompleteCalculator {
       // identify timestamp of last visible change
       const end = Math.max(start, this.lastImageLoadTimestamp, this.lastMutation?.timestamp ?? 0);
 
+      const navigationEntries = performance.getEntriesByType(
+        'navigation'
+      ) as PerformanceNavigationTiming[];
+      const navigationType = isBfCacheRestore
+        ? 'back_forward'
+        : start !== 0
+        ? 'script'
+        : navigationEntries[navigationEntries.length - 1].type;
+
       // report result to subscribers
       this.next({
         start,
         end,
         duration: end - start,
         detail: {
+          navigationType,
           didNetworkTimeOut,
           lastVisibleChange:
             this.lastImageLoadTimestamp > (this.lastMutation?.timestamp ?? 0)

test/e2e/bfcache/index.spec.ts

@@ -16,6 +16,7 @@ test.describe('TTVC', () => {
     expect(entries.length).toBe(1);
     expect(entries[0].duration).toBeGreaterThanOrEqual(PAGELOAD_DELAY);
     expect(entries[0].duration).toBeLessThanOrEqual(PAGELOAD_DELAY + FUDGE);
+    expect(entries[0].detail.navigationType).toBe('navigate');
 
     await page.goto(`/test/bfcache/about?delay=${PAGELOAD_DELAY}&cache=true`, {
       waitUntil: 'networkidle',
@@ -26,6 +27,7 @@ test.describe('TTVC', () => {
     expect(entries.length).toBe(1);
     expect(entries[0].duration).toBeGreaterThanOrEqual(PAGELOAD_DELAY);
     expect(entries[0].duration).toBeLessThanOrEqual(PAGELOAD_DELAY + FUDGE);
+    expect(entries[0].detail.navigationType).toBe('navigate');
 
     await page.goBack({waitUntil: 'networkidle'});
 
@@ -34,5 +36,6 @@ test.describe('TTVC', () => {
     // note: webkit clears previous values from this list on page restore
     expect(entries[entries.length - 1].duration).toBeGreaterThanOrEqual(0);
     expect(entries[entries.length - 1].duration).toBeLessThanOrEqual(FUDGE);
+    expect(entries[entries.length - 1].detail.navigationType).toBe('back_forward');
   });
 });