events: expose CustomEvent on the global scope via a CLI flag

.eslintrc.js

@@ -321,6 +321,7 @@ module.exports = {
     ByteLengthQueuingStrategy: 'readable',
     CompressionStream: 'readable',
     CountQueuingStrategy: 'readable',
+    CustomEvent: 'readable',
     Crypto: 'readable',
     CryptoKey: 'readable',
     DecompressionStream: 'readable',

doc/api/cli.md

@@ -280,6 +280,14 @@ effort to report stack traces relative to the original source file.
 Overriding `Error.prepareStackTrace` prevents `--enable-source-maps` from
 modifying the stack trace.
 
+### `--experimental-global-customevent`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+Expose the [CustomEvent Web API][] on the global scope.
+
 ### `--experimental-global-webcrypto`
 
 <!-- YAML
@@ -1652,6 +1660,7 @@ Node.js options that are allowed are:
 * `--enable-fips`
 * `--enable-source-maps`
 * `--experimental-abortcontroller`
+* `--experimental-global-customevent`
 * `--experimental-global-webcrypto`
 * `--experimental-import-meta-resolve`
 * `--experimental-json-modules`
@@ -2077,6 +2086,7 @@ done
 [#42511]: https://github.com/nodejs/node/issues/42511
 [Chrome DevTools Protocol]: https://chromedevtools.github.io/devtools-protocol/
 [CommonJS]: modules.md
+[CustomEvent Web API]: https://dom.spec.whatwg.org/#customevent
 [ECMAScript module loader]: esm.md#loaders
 [Fetch API]: https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API
 [Modules loaders]: packages.md#modules-loaders

doc/api/globals.md

@@ -380,6 +380,19 @@ A browser-compatible implementation of {CryptoKey}. This global is available
 only if the Node.js binary was compiled with including support for the
 `node:crypto` module.
 
+## `CustomEvent`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - Experimental. Enable this API with the
+> [`--experimental-global-customevent`][] CLI flag.
+
+<!-- type=global -->
+
+A browser-compatible implementation of the [`CustomEvent` Web API][].
+
 ## Class: `DecompressionStream`
 
 <!-- YAML
@@ -852,12 +865,14 @@ added: v18.0.0
 A browser-compatible implementation of [`WritableStreamDefaultWriter`][].
 
 [Web Crypto API]: webcrypto.md
+[`--experimental-global-customevent`]: cli.md#--experimental-global-customevent
 [`--experimental-global-webcrypto`]: cli.md#--experimental-global-webcrypto
 [`--no-experimental-fetch`]: cli.md#--no-experimental-fetch
 [`AbortController`]: https://developer.mozilla.org/en-US/docs/Web/API/AbortController
 [`ByteLengthQueuingStrategy`]: webstreams.md#class-bytelengthqueuingstrategy
 [`CompressionStream`]: webstreams.md#class-compressionstream
 [`CountQueuingStrategy`]: webstreams.md#class-countqueuingstrategy
+[`CustomEvent` Web API]: https://dom.spec.whatwg.org/#customevent
 [`DOMException`]: https://developer.mozilla.org/en-US/docs/Web/API/DOMException
 [`DecompressionStream`]: webstreams.md#class-decompressionstream
 [`EventTarget` and `Event` API]: events.md#eventtarget-and-event-api

doc/node.1

@@ -139,6 +139,9 @@ Requires Node.js to be built with
 .It Fl -enable-source-maps
 Enable Source Map V3 support for stack traces.
 .
+.It Fl -experimental-global-customevent
+Expose the CustomEvent on the global scope.
+.
 .It Fl -experimental-global-webcrypto
 Expose the Web Crypto API on the global scope.
 .

lib/.eslintrc.yaml

@@ -49,6 +49,8 @@ rules:
       message: Use `const { CompressionStream } = require('internal/webstreams/compression')` instead of the global.
     - name: CountQueuingStrategy
       message: Use `const { CountQueuingStrategy } = require('internal/webstreams/queuingstrategies')` instead of the global.
+    - name: CustomEvent
+      message: Use `const { CustomEvent } = require('internal/event_target');` instead of the global.
     - name: DecompressionStream
       message: Use `const { DecompressionStream } = require('internal/webstreams/compression')` instead of the global.
     - name: DOMException

lib/internal/bootstrap/pre_execution.js

@@ -44,6 +44,7 @@ function prepareMainThreadExecution(expandArgv1 = false,
   setupWarningHandler();
   setupFetch();
   setupWebCrypto();
+  setupCustomEvent();
 
   // Resolve the coverage directory to an absolute path, and
   // overwrite process.env so that the original path gets passed
@@ -249,6 +250,17 @@ function setupWebCrypto() {
   }
 }
 
+// TODO(daeyeon): move this to internal/bootstrap/browser when the CLI flag is
+//                removed.
+function setupCustomEvent() {
+  if (process.config.variables.node_no_browser_globals ||
+      !getOptionValue('--experimental-global-customevent')) {
+    return;
+  }
+  const { CustomEvent } = require('internal/event_target');
+  exposeInterface(globalThis, 'CustomEvent', CustomEvent);
+}
+
 // Setup User-facing NODE_V8_COVERAGE environment variable that writes
 // ScriptCoverage to a specified file.
 function setupCoverageHooks(dir) {
@@ -567,6 +579,7 @@ module.exports = {
   setupWarningHandler,
   setupFetch,
   setupWebCrypto,
+  setupCustomEvent,
   setupDebugEnv,
   setupPerfHooks,
   prepareMainThreadExecution,

lib/internal/main/worker_thread.js

@@ -19,6 +19,7 @@ const {
   setupWarningHandler,
   setupFetch,
   setupWebCrypto,
+  setupCustomEvent,
   setupDebugEnv,
   setupPerfHooks,
   initializeDeprecations,
@@ -71,6 +72,7 @@ setupDebugEnv();
 setupWarningHandler();
 setupFetch();
 setupWebCrypto();
+setupCustomEvent();
 initializeSourceMapsHandlers();
 
 // Since worker threads cannot switch cwd, we do not need to

src/node_options.cc

@@ -339,6 +339,10 @@ EnvironmentOptionsParser::EnvironmentOptionsParser() {
             &EnvironmentOptions::experimental_fetch,
             kAllowedInEnvironment,
             true);
+  AddOption("--experimental-global-customevent",
+            "expose experimental CustomEvent on the global scope",
+            &EnvironmentOptions::experimental_global_customevent,
+            kAllowedInEnvironment);
   AddOption("--experimental-global-webcrypto",
             "expose experimental Web Crypto API on the global scope",
             &EnvironmentOptions::experimental_global_web_crypto,

src/node_options.h

@@ -108,6 +108,7 @@ class EnvironmentOptions : public Options {
   std::string dns_result_order;
   bool enable_source_maps = false;
   bool experimental_fetch = true;
+  bool experimental_global_customevent = false;
   bool experimental_global_web_crypto = false;
   bool experimental_https_modules = false;
   std::string experimental_specifier_resolution;

test/common/index.js

@@ -315,6 +315,9 @@ if (hasCrypto && global.crypto) {
   knownGlobals.push(global.CryptoKey);
   knownGlobals.push(global.SubtleCrypto);
 }
+if (global.CustomEvent) {
+  knownGlobals.push(global.CustomEvent);
+}
 if (global.ReadableStream) {
   knownGlobals.push(
     global.ReadableStream,

test/parallel/test-global-customevent.js

@@ -0,0 +1,11 @@
+// Flags: --experimental-global-customevent --expose-internals
+'use strict';
+
+require('../common');
+const { strictEqual, ok } = require('node:assert');
+const { CustomEvent: internalCustomEvent } = require('internal/event_target');
+
+// Global
+ok(CustomEvent);
+
+strictEqual(CustomEvent, internalCustomEvent);