chore: remove unload event from OTLPExporterBrowserBase (#4438)

* Add the ability for the implementation to provide the binding event for shutdown.

* fix: whoops totally missed the linting formatting fix step

* Remove any concept of a shutdown event

* add change log and obey interface

* no longer need globalthis

* modify the correct changelog and identify this as a breaking change under the scenario in comments

* markdown lint

* Update experimental/CHANGELOG.md

Co-authored-by: Marc Pichler <marc.pichler@dynatrace.com>

---------

Co-authored-by: Marc Pichler <marc.pichler@dynatrace.com>

experimental/CHANGELOG.md

@@ -6,6 +6,13 @@ All notable changes to experimental packages in this project will be documented
 
 ### :boom: Breaking Change
 
+* fix(otlp-exporter-base)!: remove unload event from OTLPExporterBrowserBase [#4438](https://github.com/open-telemetry/opentelemetry-js/pull/4438) @eldavojohn
+  * Reason: The 'unload' event prevents sites from taking advantage of Google's [backward/forward cache](https://web.dev/articles/bfcache#never_use_the_unload_event) and will be [deprecated](https://developer.chrome.com/articles/deprecating-unload/).  It is now up to the consuming site to implement these shutdown events.
+  * This breaking change affects users under this scenario:
+    1. A user extends the exporter and overrides the shutdown function, and does something which is usually called by the unload listener
+    2. We remove the unload event listener
+    3. That user's overridden shutdown function no longer gets called
+
 ### :rocket: (Enhancement)
 
 * feat(instrumentation): allow LoggerProvider to be specified in Instrumentations [#4314](https://github.com/open-telemetry/opentelemetry-js/pull/4314) @hectorhdzg

experimental/packages/otlp-exporter-base/src/platform/browser/OTLPExporterBrowserBase.ts

@@ -20,7 +20,7 @@ import * as otlpTypes from '../../types';
 import { parseHeaders } from '../../util';
 import { sendWithBeacon, sendWithXhr } from './util';
 import { diag } from '@opentelemetry/api';
-import { getEnv, baggageUtils, _globalThis } from '@opentelemetry/core';
+import { getEnv, baggageUtils } from '@opentelemetry/core';
 
 /**
  * Collector Metric Exporter abstract base class
@@ -52,13 +52,9 @@ export abstract class OTLPExporterBrowserBase<
     }
   }
 
-  onInit(): void {
-    _globalThis.addEventListener('unload', this.shutdown);
-  }
+  onInit(): void {}
 
-  onShutdown(): void {
-    _globalThis.removeEventListener('unload', this.shutdown);
-  }
+  onShutdown(): void {}
 
   send(
     items: ExportItem[],