diff --git a/packager/react-packager/src/ModuleGraph/output/__tests__/util-test.js b/packager/react-packager/src/ModuleGraph/output/__tests__/util-test.js
new file mode 100644
index 00000000000000..5704a90f33f091
--- /dev/null
+++ b/packager/react-packager/src/ModuleGraph/output/__tests__/util-test.js
@@ -0,0 +1,83 @@
+/**
+ * Copyright (c) 2016-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+'use strict';
+
+jest.disableAutomock();
+
+const {match} = require('sinon');
+const {fn} = require('../../test-helpers');
+const {
+  addModuleIdsToModuleWrapper,
+  createIdForPathFn,
+} = require('../util');
+
+const {any} = jasmine;
+
+describe('`addModuleIdsToModuleWrapper`:', () => {
+  const path = 'path/to/file';
+  const createModule = (dependencies = []) => ({
+    dependencies,
+    file: {code: '__d(function(){});', isModule: true, path},
+  });
+
+  it('completes the module wrapped with module ID, and an array of dependency IDs', () => {
+    const dependencies = [
+      {id: 'a', path: 'path/to/a.js'},
+      {id: 'b', path: 'location/of/b.js'},
+    ];
+    const module = createModule(dependencies);
+
+    const idForPath = fn();
+    idForPath.stub
+      .withArgs(match({path})).returns(12)
+      .withArgs(match({path: dependencies[0].path})).returns(345)
+      .withArgs(match({path: dependencies[1].path})).returns(6);
+
+    expect(addModuleIdsToModuleWrapper(module, idForPath))
+      .toEqual('__d(function(){}, 12, [345, 6]);');
+  });
+
+  it('omits the array of dependency IDs if it is empty', () => {
+    const module = createModule();
+    expect(addModuleIdsToModuleWrapper(module, () => 98))
+      .toEqual(`__d(function(){}, ${98});`);
+  });
+});
+
+describe('`createIdForPathFn`', () => {
+  let idForPath;
+  beforeEach(() => {
+    idForPath = createIdForPathFn();
+  });
+
+  it('returns a number for a string', () => {
+    expect(idForPath({path: 'arbitrary'})).toEqual(any(Number));
+  });
+
+  it('returns consecutive numbers', () => {
+    const strings = [
+      'arbitrary string',
+      'looking/like/a/path',
+      '/absolute/path/to/file.js',
+      '/more files/are here',
+    ];
+
+    strings.forEach((string, i) => {
+      expect(idForPath({path: string})).toEqual(i);
+    });
+  });
+
+  it('returns the same id if the same string is passed in again', () => {
+    const path = 'this/is/an/arbitrary/path.js';
+    const id = idForPath({path});
+    idForPath({path: '/other/file'});
+    idForPath({path: 'and/another/file'});
+    expect(idForPath({path})).toEqual(id);
+  });
+});
diff --git a/packager/react-packager/src/ModuleGraph/output/util.js b/packager/react-packager/src/ModuleGraph/output/util.js
new file mode 100644
index 00000000000000..d883a748d0fadb
--- /dev/null
+++ b/packager/react-packager/src/ModuleGraph/output/util.js
@@ -0,0 +1,52 @@
+/**
+ * Copyright (c) 2016-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @flow
+ */
+'use strict';
+
+import type {Module} from '../types.flow';
+
+// Transformed modules have the form
+//   __d(function(require, module, global, exports, dependencyMap) {
+//       /* code */
+//   });
+//
+// This function adds the numeric module ID, and an array with dependencies of
+// the dependencies of the module before the closing parenthesis.
+exports.addModuleIdsToModuleWrapper = (
+  module: Module,
+  idForPath: {path: string} => number,
+): string => {
+  const {dependencies, file} = module;
+  const {code} = file;
+  const index = code.lastIndexOf(')');
+  const depencyIds =
+    dependencies.length ? `, [${dependencies.map(idForPath).join(', ')}]` : '';
+  return (
+    code.slice(0, index) +
+    `, ${idForPath(file)}` +
+    depencyIds +
+    code.slice(index)
+  );
+};
+
+// Creates an idempotent function that returns numeric IDs for objects based
+// on their `path` property.
+exports.createIdForPathFn = (): ({path: string} => number) => {
+  const seen = new Map();
+  let next = 0;
+  return ({path}) => {
+    let id = seen.get(path);
+    if (id == null) {
+      id = next++;
+      seen.set(path, id);
+    }
+    return id;
+  };
+};