doc: fix module syncBuiltinESMExports example

Fix failing code and add explanations of each assert.
PR-URL: #34284
Reviewed-By: Guy Bedford <guybedford@gmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>

Author: bmacnaughton

doc/api/module.md

@@ -87,21 +87,29 @@ does not add or remove exported names from the [ES Modules][].
 
 ```js
 constfs=require('fs');
+constassert=require('assert');
 const { syncBuiltinESMExports } =require('module');
 
-fs.readFile=null;
+fs.readFile=newAPI;
 
 deletefs.readFileSync;
 
-fs.newAPI=functionnewAPI() {
+functionnewAPI() {
 // ...
-};
+}
+
+fs.newAPI= newAPI;
 
 syncBuiltinESMExports();
 
 import('fs').then((esmFS) => {
-assert.strictEqual(esmFS.readFile, null);
-assert.strictEqual('readFileSync'in fs, true);
+// It syncs the existing readFile property with the new value
+assert.strictEqual(esmFS.readFile, newAPI);
+// readFileSync has been deleted from the required fs
+assert.strictEqual('readFileSync'in fs, false);
+// syncBuiltinESMExports() does not remove readFileSync from esmFS
+assert.strictEqual('readFileSync'in esmFS, true);
+// syncBuiltinESMExports() does not add names
 assert.strictEqual(esmFS.newAPI, undefined);
 });
 ```