Add Module._extensions (#5998)

Co-authored-by: Jarred Sumner <709451+Jarred-Sumner@users.noreply.github.com>

2 files changed, 14 insertions, 2 deletions

diff --git a/src/bun.js/modules/NodeModuleModule.h b/src/bun.js/modules/NodeModuleModule.h
index b3c34eb5e..6d8654024 100644
--- a/src/bun.js/modules/NodeModuleModule.h
+++ b/src/bun.js/modules/NodeModuleModule.h
@@ -330,13 +330,18 @@ DEFINE_NATIVE_MODULE(NodeModule) {
     exportNames.append(name);
     exportValues.append(value);
   };
-  exportNames.reserveCapacity(15);
-  exportValues.ensureCapacity(15);
+  exportNames.reserveCapacity(16);
+  exportValues.ensureCapacity(16);
   exportNames.append(vm.propertyNames->defaultKeyword);
   exportValues.append(defaultObject);
 
   put(Identifier::fromString(vm, "Module"_s), defaultObject);
 
+  // Module._extensions === require.extensions
+  put(Identifier::fromString(vm, "_extensions"_s),
+      globalObject->requireFunctionUnbound()->get(
+          globalObject, Identifier::fromString(vm, "extensions"_s)));
+
   defaultObject->putDirectCustomAccessor(
       vm, JSC::Identifier::fromString(vm, "_resolveFilename"_s),
       JSC::CustomGetterSetter::create(vm, get_resolveFilename,
diff --git a/test/js/node/module/node-module-module.test.js b/test/js/node/module/node-module-module.test.js
index 1363636ac..26fbb6fab 100644
--- a/test/js/node/module/node-module-module.test.js
+++ b/test/js/node/module/node-module-module.test.js
@@ -87,3 +87,10 @@ test("Module.prototype._compile", () => {
   expect(fn).toBe("/file/path/goes/here.js");
   expect(dn).toBe("/file/path/goes");
 });
+
+test("Module._extensions", () => {
+  expect(".js" in Module._extensions).toBeTrue();
+  expect(".json" in Module._extensions).toBeTrue();
+  expect(".node" in Module._extensions).toBeTrue();
+  expect(require.extensions).toBe(Module._extensions);
+});