doc: add esm alternative for require.main

doc/api/esm.md

@@ -928,6 +928,26 @@ hooks can provide this workflow in the future.
 
 `require.cache` is not used by `import`. It has a separate cache.
 
+### No `require.main`
+
+To detect when an ES module is run directly with Node.js, it is possible to
+compare the [`import.meta.url`][] value to the command line arguments. For
+example:
+
+```js
+import { fileURLToPath } from 'url';
+import process from 'process';
+
+if (process.argv[1] === fileURLToPath(import.meta.url)) {
+  // The script was run directly.
+}
+```
+
+The above approach does not cover the case where the script is run without the
+`.js` extension (e.g. `node script` instead of `node script.js`). These cases
+could be normalized by trimming any extension from the `import.meta.url` and
+`process.argv[1]` values.
+
 ### URL-based paths
 
 ES modules are resolved and cached based upon

doc/api/modules.md

@@ -78,6 +78,9 @@ Because `module` provides a `filename` property (normally equivalent to
 `__filename`), the entry point of the current application can be obtained
 by checking `require.main.filename`.
 
+When running [ECMAScript Modules][], `require.main` is not available. See the
+ECMAScript Modules documentation for a possible [`require.main` alternative][].
+
 ## Addenda: Package manager tips
 
 <!-- type=misc -->
@@ -1148,3 +1151,4 @@ consists of the following keys:
 [`Error.prepareStackTrace(error, trace)`]: https://v8.dev/docs/stack-trace-api#customizing-stack-traces
 [`SourceMap`]: modules.html#modules_class_module_sourcemap
 [Source map v3 format]: https://sourcemaps.info/spec.html#h.mofvlxcwqzej
+[`require.main` alternative]: esm.html#esm_no_require_main