[Feature] Allow providing your own implementation of fetch Salesforce…

…CommerceCloud#159

src/static/helpers/environment.ts

@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: BSD-3-Clause
  * For full license text, see the LICENSE file in the repo root or https://opensource.org/licenses/BSD-3-Clause
  */
-import type {FetchFunction} from '../clientConfig';
+import type {FetchFunction, FetchOptions} from '../clientConfig';
 
 /*
  * Copyright (c) 2022, Salesforce, Inc.
@@ -24,6 +24,8 @@ export const globalObject = isBrowser ? window : globalThis;
 
 export const hasFetchAvailable = typeof globalObject.fetch === 'function';
 
+let lazyFetch: FetchFunction;
+
 // eslint-disable-next-line @typescript-eslint/no-unsafe-assignment
 export const fetch: FetchFunction = (() => {
   if (isNode) {
@@ -38,6 +40,13 @@ export const fetch: FetchFunction = (() => {
     throw new Error(
       'Bad environment: it is not a node environment but fetch is not defined'
     );
-
-  return globalObject.fetch;
+  return (
+    input: RequestInfo,
+    init?: FetchOptions | undefined
+  ): Promise<Response> => {
+    if (!lazyFetch) {
+      lazyFetch = globalObject.fetch;
+    }
+    return lazyFetch.apply(globalObject, [input, init]);
+  };
 })();