Replace the test helper class Deferred with polyfilled `Promise.wit…

…hResolvers`.

changelog.md

@@ -41,6 +41,7 @@
 - Integrated a new dev dependency [`eslint-plugin-jsdoc`](https://npm.im/eslint-plugin-jsdoc) and revised types.
 - Removed the Node.js CLI option `--unhandled-rejections=throw` in the package script `tests` as it’s now the default for all supported Node.js versions.
 - Avoid hardcoding a default value in the type `FileUploadCreateReadStreamOptions` property `highWaterMark` description and use the function `getDefaultHighWaterMark` from `node:stream` in tests.
+- Replaced the test helper class `Deferred` with polyfilled `Promise.withResolvers`.
 - Omit unused catch bindings in the function `processRequest`.
 - Corrected the JSDoc type `FileUploadCreateReadStreamOptions` in the module `processRequest.mjs`.
 - Avoid using `return` in the middleware.

processRequest.test.mjs

@@ -1,6 +1,7 @@
 // @ts-check
 
 import "./test/polyfillFile.mjs";
+import "./test/polyfillPromiseWithResolvers.mjs";
 
 import {
   deepStrictEqual,
@@ -20,7 +21,6 @@ import { ReadStream } from "fs-capacitor";
 
 import processRequest from "./processRequest.mjs";
 import abortingMultipartRequest from "./test/abortingMultipartRequest.mjs";
-import Deferred from "./test/Deferred.mjs";
 import Upload from "./Upload.mjs";
 
 describe(
@@ -794,11 +794,15 @@ describe(
       // request part way through, the server request handler must be manually
       // awaited or else the test will resolve and the process will exit before
       // it’s done.
-      const done = new Deferred();
+
+      /** @type {PromiseWithResolvers<void>} */
+      const done = Promise.withResolvers();
 
       // The request must be aborted after it has been received by the server
       // request handler, or else Node.js won’t run the handler.
-      const requestReceived = new Deferred();
+
+      /** @type {PromiseWithResolvers<void>} */
+      const requestReceived = Promise.withResolvers();
 
       const server = createServer(async (request, response) => {
         try {
@@ -936,11 +940,15 @@ describe(
       // request part way through, the server request handler must be manually
       // awaited or else the test will resolve and the process will exit before
       // it’s done.
-      const done = new Deferred();
+
+      /** @type {PromiseWithResolvers<void>} */
+      const done = Promise.withResolvers();
 
       // The request must be aborted after it has been received by the server
       // request handler, or else Node.js won’t run the handler.
-      const requestReceived = new Deferred();
+
+      /** @type {PromiseWithResolvers<void>} */
+      const requestReceived = Promise.withResolvers();
 
       const server = createServer(async (request, response) => {
         try {

test/polyfillPromiseWithResolvers.mjs

@@ -0,0 +1,20 @@
+// @ts-check
+
+// TODO: Delete this polyfill once all supported Node.js versions implement
+// `Promise.withResolvers`.
+Promise.withResolvers ??= () => new PromiseWithResolversReturn();
+
+/**
+ * A promise with resolvers.
+ * @template T
+ * @implements {PromiseWithResolvers<T>}
+ */
+class PromiseWithResolversReturn {
+  constructor() {
+    /** @type {Promise<T>} */
+    this.promise = new Promise((resolve, reject) => {
+      this.resolve = resolve;
+      this.reject = reject;
+    });
+  }
+}