add debug warning for fetch api

Author: AbhiPrasad

MIGRATION.md

@@ -90,6 +90,10 @@ to access and mutate the current scope.
 
 `@sentry/hub` has been removed. All exports from `@sentry.hub` should be available in `@sentry/core`.
 
+## Removal of `makeXHRTransport` transport (#10703)
+
+The `makeXHRTransport` transport has been removed. Only `makeFetchTransport` is available now. This means that the Sentry SDK requires the fetch API to be available in the environment.
+
 ## General API Changes
 
 - The minumum supported Node version for all the SDK packages is Node 14 (#10527)

packages/browser/src/sdk.ts

@@ -9,7 +9,12 @@ import {
   startSession,
 } from '@sentry/core';
 import type { DsnLike, Integration, Options, UserFeedback } from '@sentry/types';
-import { addHistoryInstrumentationHandler, logger, stackParserFromStackParserOptions } from '@sentry/utils';
+import {
+  addHistoryInstrumentationHandler,
+  logger,
+  stackParserFromStackParserOptions,
+  supportsFetch,
+} from '@sentry/utils';
 
 import type { BrowserClientOptions, BrowserOptions } from './client';
 import { BrowserClient } from './client';
@@ -118,6 +123,13 @@ export function init(options: BrowserOptions = {}): void {
     options.sendClientReports = true;
   }
 
+  if (DEBUG_BUILD) {
+    if (!supportsFetch()) {
+      logger.warn(
+        'No Fetch API detected. The Sentry SDK requires a Fetch API compatible environment to send events. Please add a Fetch API polyfill.',
+      );
+    }
+  }
   const clientOptions: BrowserClientOptions = {
     ...options,
     stackParser: stackParserFromStackParserOptions(options.stackParser || defaultStackParser),