module: add --module option

lib/internal/modules/esm/get_format.js

@@ -16,6 +16,7 @@ const {
 
 const experimentalNetworkImports =
   getOptionValue('--experimental-network-imports');
+const isESModule = !!getOptionValue('--module');
 const { getPackageType, getPackageScopeConfig } = require('internal/modules/esm/resolve');
 const { fileURLToPath } = require('internal/url');
 const { ERR_UNKNOWN_FILE_EXTENSION } = require('internal/errors').codes;
@@ -73,6 +74,9 @@ function extname(url) {
  * @returns {string}
  */
 function getFileProtocolModuleFormat(url, context, ignoreErrors) {
+  if (isESModule && context.parentURL === undefined)
+    return 'module';
+
   const ext = extname(url);
   if (ext === '.js') {
     return getPackageType(url) === 'module' ? 'module' : 'commonjs';

lib/internal/modules/run_main.js

@@ -46,12 +46,12 @@ function shouldUseESMLoader(mainPath) {
   return pkg && pkg.data.type === 'module';
 }
 
-function runMainESM(mainPath) {
+function runMainESM(mainPath, isPath = true) {
   const { loadESM } = require('internal/process/esm_loader');
   const { pathToFileURL } = require('internal/url');
 
   handleMainPromise(loadESM((esmLoader) => {
-    const main = path.isAbsolute(mainPath) ?
+    const main = isPath && path.isAbsolute(mainPath) ?
       pathToFileURL(mainPath).href : mainPath;
     return esmLoader.import(main, undefined, { __proto__: null });
   }));
@@ -73,6 +73,13 @@ async function handleMainPromise(promise) {
 // monkey-patchable code that belongs to the CJS loader (exposed by
 // `require('module')`) even when the entry point is ESM.
 function executeUserEntryPoint(main = process.argv[1]) {
+  const mainModule = getOptionValue('--module');
+  if (mainModule) {
+    const { pathToFileURL, URL } = require('internal/url');
+    const mainModuleURL = new URL(mainModule, pathToFileURL(process.cwd() + path.sep)).href;
+    return void runMainESM(mainModuleURL, false);
+  }
+
   const resolvedMain = resolveMainPath(main);
   const useESMLoader = shouldUseESMLoader(resolvedMain);
   if (useESMLoader) {

src/node.cc

@@ -360,7 +360,8 @@ MaybeLocal<Value> StartExecution(Environment* env, StartExecutionCallback cb) {
     return StartExecution(env, "internal/main/watch_mode");
   }
 
-  if (!first_argv.empty() && first_argv != "-") {
+  if ((!first_argv.empty() && first_argv != "-") ||
+      env->options()->main_esm_module != "") {
     return StartExecution(env, "internal/main/run_main_module");
   }
 

src/node_options.cc

@@ -701,6 +701,9 @@ EnvironmentOptionsParser::EnvironmentOptionsParser() {
             "ES module to preload (option can be repeated)",
             &EnvironmentOptions::preload_esm_modules,
             kAllowedInEnvvar);
+  AddOption("--module",
+            "Main ES module to load by absolute or relative URL",
+            &EnvironmentOptions::main_esm_module);
   AddOption("--interactive",
             "always enter the REPL even if stdin does not appear "
             "to be a terminal",

src/node_options.h

@@ -211,6 +211,8 @@ class EnvironmentOptions : public Options {
 
   std::vector<std::string> preload_esm_modules;
 
+  std::string main_esm_module;
+
   std::vector<std::string> user_argv;
 
   inline DebugOptions* get_debug_options() { return &debug_options_; }