fix(fetch): use current global fetch instead of cached one when env fetch is not specified to keep MSW support; (#7030)

lib/adapters/fetch.js

@@ -12,9 +12,9 @@ const DEFAULT_CHUNK_SIZE = 64 * 1024;
 
 const {isFunction} = utils;
 
-const globalFetchAPI = (({fetch, Request, Response}) => ({
+const globalFetchAPI = (({Request, Response}) => ({
-    fetch, Request, Response
+  Request, Response
-  }))(utils.global);
+}))(utils.global);
 
 const {
   ReadableStream, TextEncoder
@@ -30,8 +30,12 @@ const test = (fn, ...args) => {
 }
 
 const factory = (env) => {
-  const {fetch, Request, Response} = Object.assign({}, globalFetchAPI, env);
+  env = utils.merge.call({
-  const isFetchSupported = isFunction(fetch);
+    skipUndefined: true
+  }, globalFetchAPI, env);
+
+  const {fetch: envFetch, Request, Response} = env;
+  const isFetchSupported = envFetch ? isFunction(envFetch) : typeof fetch === 'function';
   const isRequestSupported = isFunction(Request);
   const isResponseSupported = isFunction(Response);
 
@@ -134,6 +138,8 @@ const factory = (env) => {
       fetchOptions
     } = resolveConfig(config);
 
+    let _fetch = envFetch || fetch;
+
     responseType = responseType ? (responseType + '').toLowerCase() : 'text';
 
     let composedSignal = composeSignals([signal, cancelToken && cancelToken.toAbortSignal()], timeout);
@@ -193,7 +199,7 @@ const factory = (env) => {
 
       request = isRequestSupported && new Request(url, resolvedOptions);
 
-      let response = await (isRequestSupported ? fetch(request, fetchOptions) : fetch(url, resolvedOptions));
+      let response = await (isRequestSupported ? _fetch(request, fetchOptions) : _fetch(url, resolvedOptions));
 
       const isStreamResponse = supportsResponseStream && (responseType === 'stream' || responseType === 'response');
 
@@ -256,12 +262,8 @@ const factory = (env) => {
 const seedCache = new Map();
 
 export const getFetch = (config) => {
-  let env = utils.merge.call({
+  let env = config ? config.env : {};
-    skipUndefined: true
-  }, globalFetchAPI, config ? config.env : null);
-
   const {fetch, Request, Response} = env;
-
   const seeds = [
     Request, Response, fetch
   ];

test/unit/adapters/fetch.js

@@ -489,5 +489,32 @@ describe('supports fetch with nodejs', function () {
 
       assert.strictEqual(data, 'OK');
     });
+
+    it('should use current global fetch when env fetch is not specified', async() => {
+      const globalFetch = fetch;
+
+      fetch = async () => {
+        return {
+          headers: {
+            foo: '1'
+          },
+          text: async () => 'global'
+        }
+      };
+
+      try {
+        server = await startHTTPServer((req, res) => res.end('OK'));
+
+        const {data} = await fetchAxios.get('/', {
+          env: {
+            fetch: undefined
+          }
+        });
+
+        assert.strictEqual(data, 'global');
+      } finally {
+        fetch = globalFetch;
+      }
+    });
   });
 });