Fix batching after page navigation

.changeset/orange-actors-hug.md

@@ -0,0 +1,5 @@
+---
+'@segment/analytics-next': patch
+---
+
+Fix batching after page navigation

.github/PULL_REQUEST_TEMPLATE

@@ -8,5 +8,4 @@ Hello! And thanks for contributing to the Analytics-Next 🎉
 Also make sure to describe how you tested this change, include any gifs or screenshots you find necessary.
 --->
 
-
-[] I've included a changeset (psst. run `yarn changeset`. Read about changesets [here](https://github.com/changesets/changesets/blob/main/docs/adding-a-changeset.md)).
+- [ ] I've included a changeset (psst. run `yarn changeset`. Read about changesets [here](https://github.com/changesets/changesets/blob/main/docs/adding-a-changeset.md)).

packages/browser/src/lib/__tests__/on-page-leave.test.ts → packages/browser/src/lib/__tests__/on-page-change.test.ts

@@ -1,4 +1,4 @@
-import { onPageLeave } from '../on-page-leave'
+import { onPageChange } from '../on-page-change'
 
 const helpers = {
   dispatchEvent(event: 'pagehide' | 'visibilitychange') {
@@ -24,42 +24,51 @@ beforeEach(() => {
   helpers.setVisibilityState('visible')
 })
 
-describe('onPageLeave', () => {
+describe('onPageChange', () => {
   test('callback should fire on pagehide', () => {
     const cb = jest.fn()
-    onPageLeave(cb)
+    onPageChange(cb)
     helpers.dispatchPageHideEvent()
     expect(cb).toBeCalledTimes(1)
   })
 
   test('callback should fire if document becomes hidden', () => {
     const cb = jest.fn()
-    onPageLeave(cb)
+    onPageChange(cb)
     helpers.dispatchVisChangeEvent('hidden')
     expect(cb).toBeCalledTimes(1)
   })
 
-  test('callback should *not* fire if document becomes visible', () => {
+  test('callback should fire if document becomes visible', () => {
     const cb = jest.fn()
-    onPageLeave(cb)
+    onPageChange(cb)
     helpers.dispatchVisChangeEvent('visible')
-    expect(cb).not.toBeCalled()
+    expect(cb).toBeCalledTimes(1)
   })
 
   test('if both event handlers fire, callback should still fire only once', () => {
     const cb = jest.fn()
-    onPageLeave(cb)
+    onPageChange(cb)
     helpers.dispatchVisChangeEvent('hidden')
     helpers.dispatchPageHideEvent()
     expect(cb).toBeCalledTimes(1)
   })
 
-  test('if user leaves a tab, returns, and leaves again, callback should be called on each departure', () => {
+  test('if user leaves a tab, returns, and leaves again, callback should be called on each navigation', () => {
     const cb = jest.fn()
-    onPageLeave(cb)
+    onPageChange(cb)
     helpers.dispatchVisChangeEvent('hidden')
     helpers.dispatchVisChangeEvent('visible')
     helpers.dispatchVisChangeEvent('hidden')
-    expect(cb).toBeCalledTimes(2)
+    expect(cb).toBeCalledTimes(3)
+  })
+
+  test('if user navigates, callback should be passed appropriate "unloaded" value', () => {
+    const cb = jest.fn()
+    onPageChange(cb)
+    helpers.dispatchVisChangeEvent('hidden')
+    expect(cb).toBeCalledWith(true)
+    helpers.dispatchVisChangeEvent('visible')
+    expect(cb).toBeCalledWith(false)
   })
 })

packages/browser/src/lib/on-page-leave.ts → packages/browser/src/lib/on-page-change.ts

@@ -7,23 +7,23 @@
  *
  * adapted from https://stackoverflow.com/questions/3239834/window-onbeforeunload-not-working-on-the-ipad/52864508#52864508,
  */
-export const onPageLeave = (cb: (...args: unknown[]) => void) => {
+export const onPageChange = (cb: (...args: boolean[]) => void) => {
   let unloaded = false // prevents double firing if both are supported
 
   window.addEventListener('pagehide', () => {
     if (unloaded) return
     unloaded = true
-    cb()
+    cb(unloaded)
   })
 
   // using document instead of window because of bug affecting browsers before safari 14 (detail in footnotes https://caniuse.com/?search=visibilitychange)
   document.addEventListener('visibilitychange', () => {
     if (document.visibilityState == 'hidden') {
       if (unloaded) return
       unloaded = true
-      cb()
     } else {
       unloaded = false
     }
+    cb(unloaded)
   })
 }

packages/browser/src/plugins/segmentio/batched-dispatcher.ts

@@ -1,6 +1,6 @@
 import { SegmentEvent } from '../../core/events'
 import { fetch } from '../../lib/fetch'
-import { onPageLeave } from '../../lib/on-page-leave'
+import { onPageChange } from '../../lib/on-page-change'
 
 export type BatchingDispatchConfig = {
   size?: number
@@ -91,10 +91,10 @@ export default function batch(
     }, timeout)
   }
 
-  onPageLeave(() => {
-    pageUnloaded = true
+  onPageChange((unloaded: boolean) => {
+    pageUnloaded = unloaded
 
-    if (buffer.length) {
+    if (pageUnloaded && buffer.length) {
       const reqs = chunks(buffer).map(sendBatch)
       Promise.all(reqs).catch(console.error)
     }