lib: refactor lazy loading of undici for fetch method

lib/internal/bootstrap/web/exposed-window-or-worker.js

@@ -57,32 +57,21 @@ defineReplaceableLazyAttribute(globalThis, 'perf_hooks', ['performance']);
 const { installObjectURLMethods } = require('internal/url');
 installObjectURLMethods();
 
-{
- // https://fetch.spec.whatwg.org/#fetch-method
- function set(value) {
- ObjectDefineProperty(globalThis, 'fetch', {
- __proto__: null,
- writable: true,
- value,
- });
- }
- ObjectDefineProperty(globalThis, 'fetch', {
- __proto__: null,
- configurable: true,
- enumerable: true,
- set,
- get() {
- function fetch(input, init = undefined) {
- // Loading undici alone lead to promises which breaks lots of tests so we
- // have to load it really lazily for now.
- const { fetch: impl } = require('internal/deps/undici/undici');
- return impl(input, init);
- }
- set(fetch);
- return fetch;
- },
- });
-}
+let fetchImpl;
+// https://fetch.spec.whatwg.org/#fetch-method
+ObjectDefineProperty(globalThis, 'fetch', {
+ __proto__: null,
+ configurable: true,
+ enumerable: true,
+ writable: true,
+ value: function value(input, init = undefined) {
+ if (!fetchImpl) { // Implement lazy loading of undici module for fetch function
+ const undiciModule = require('internal/deps/undici/undici');
+ fetchImpl = undiciModule.fetch;
+ }
+ return fetchImpl(input, init);
+ },
+});
 
 // https://xhr.spec.whatwg.org/#interface-formdata
 // https://fetch.spec.whatwg.org/#headers-class

test/parallel/test-fetch-mock.js

@@ -0,0 +1,20 @@
+'use strict';
+require('../common');
+const { mock, test } = require('node:test');
+const assert = require('node:assert');
+
+test('should correctly stub globalThis.fetch', async () => {
+ const customFetch = async (url) => {
+ return {
+ text: async () => 'foo',
+ };
+ };
+
+ mock.method(globalThis, 'fetch', customFetch);
+
+ const response = await globalThis.fetch('some-url');
+ const text = await response.text();
+
+ assert.strictEqual(text, 'foo');
+ mock.restoreAll();
+});