This PR was originally submitted to React Native project when bundler was part of that and it was suggested to merge with this project.

Link to original request
facebook/react-native#13980

…to their reliance on some CommonJS/node module behavior not implemented by the React Native require polyfill from the packager.

This PR adds some of these behaviors:

Circular dependencies when exporting by assignment to the module.exports object. Should fix #3298 for good.
Exporting by assignment to this object. Fixes #2862
The module.id represents a unique identifier that can be used in require() calls.
There were no tests for the require polyfill so I added one.

Motivation (required)

What existing problem does the pull request solve?
Circular dependencies when exporting by assignment to the module.exports object. Should fix #3298 for good.
Exporting by assignment to this object. Fixes #2862

Test Plan (required)

There is no change to UI or API. However, tests have been added for require.js polyfill.

Next Steps

Individual and company CLA have been signed already.

Author: cgupta-logmein

package.json

@@ -59,7 +59,6 @@
     "timers": "fake",
     "setupFiles": [
       "<rootDir>/scripts/setupJest.js"
-    ],
-    "testEnvironment": "node"
+    ]
   }
 }

packages/metro-bundler/src/Resolver/polyfills/__tests__/require-test.js

@@ -14,6 +14,13 @@
 
 'use strict';
 
+// TODO: figure out why jest.resetModules() doesn't reset the polyfill's module cache
+global.__DEV__ = false;
+const origGlobalRequire = global.require;
+require('../require');
+const requireShim = global.require;
+const defineShim = global.__d;
+global.require = origGlobalRequire;
 const babel = require('babel-core');
 const babelConfig = require('../../../babelRegisterOnly').config;
 const fs = require('fs');
@@ -102,4 +109,121 @@ describe('require', () => {
       expect(mockFactory.mock.calls[0][4]).toEqual([2, 3]);
     });
   });
+  describe('exports', () => {
+    it('should be an object containing named exports', () => {
+      defineShim(function(global, require, module, exports) {
+        expect(exports).toEqual({});
+        exports.hello = 'world';
+      }, 1);
+      expect(requireShim(1)).toEqual({hello: 'world'});
+    });
+  });
+
+  describe('this', () => {
+    it('should be the exports object', () => {
+      defineShim(function(global, require, module, exports) {
+        expect(this).toBe(exports);
+      }, 2);
+      requireShim(2);
+    });
+  });
+
+  describe('module.id', () => {
+    it('should be the identifier of the module passed to require', () => {
+      defineShim(function(global, require, module, exports) {
+        expect(module.id).toBe(3);
+      }, 3);
+      requireShim(3);
+    });
+  });
+
+  describe('module.exports', () => {
+    it('should be the same as exports', () => {
+      defineShim(function(global, require, module, exports) {
+        expect(module.exports).toBe(exports);
+      }, 11);
+      requireShim(11);
+    });
+
+    describe('should support re-assignements', () => {
+      let moduleId = 21;
+      function testModuleExportsValue(value) {
+        defineShim(function(global, require, module, exports) {
+          module.exports = value;
+        }, moduleId);
+        expect(requireShim(moduleId)).toBe(value);
+        moduleId++;
+      }
+
+      it('to a primitive value', () => {
+        testModuleExportsValue(123);
+      });
+
+      it('to an object', () => {
+        testModuleExportsValue({
+          hello: 'world',
+        });
+      });
+
+      it('to a function', () => {
+        testModuleExportsValue(function Test() {});
+      });
+    });
+  });
+
+  describe('dependencies', () => {
+    it('should be resolved', () => {
+      defineShim(function(global, require, module, exports) {
+        exports.dep2 = require(32);
+      }, 31);
+      defineShim(function(global, require, module, exports) {
+        exports.hello = 'world';
+      }, 32);
+      expect(requireShim(31)).toEqual({
+        dep2: {
+          hello: 'world',
+        },
+      });
+    });
+
+    it('should handle circular deps using exports', () => {
+      defineShim(function(global, require, module, exports) {
+        exports.first = 'first value';
+        var p = require(42).p;
+        exports.first = 'second value';
+        exports.firstWas = p();
+      }, 41);
+      defineShim(function(global, require, module, exports) {
+        var first = require(41).first;
+        exports.p = function() {
+          return first;
+        };
+      }, 42);
+      expect(requireShim(41)).toEqual({
+        first: 'second value',
+        firstWas: 'first value',
+      });
+    });
+
+    it('should handle circular deps using module.exports', () => {
+      defineShim(function(global, require, module, exports) {
+        module.exports = {
+          first: 'first value',
+        };
+        var p = require(52).p;
+        module.exports.first = 'second value';
+        module.exports.firstWas = p();
+      }, 51);
+      defineShim(function(global, require, module, exports) {
+        var first = require(51).first;
+        exports.p = function() {
+          return first;
+        };
+      }, 52);
+      expect(requireShim(51)).toEqual({
+        first: 'second value',
+        firstWas: 'first value',
+      });
+    });
+  });
 });

packages/metro-bundler/src/Resolver/polyfills/require.js

@@ -176,23 +176,46 @@ function loadModuleImplementation(moduleId, module) {
   // factory to keep any require cycles inside the factory from causing an
   // infinite require loop.
   module.isInitialized = true;
-  const exports = (module.exports = {});
+  module.exports = {};
   const {factory, dependencyMap} = module;
   try {
     if (__DEV__) {
       // $FlowFixMe: we know that __DEV__ is const and `Systrace` exists
       Systrace.beginEvent('JS_require_' + (module.verboseName || moduleId));
     }
 
-    const moduleObject: Module = {exports};
+    const moduleObject: Module = {
+      get id() {
+        return moduleId;
+      },
+      get hot() {
+        return module.hot;
+      },
+      set hot(value) {
+        module.hot = value;
+      },
+      get exports() {
+        return module.exports;
+      },
+      set exports(value) {
+        module.exports = value;
+      },
+    };
     if (__DEV__ && module.hot) {
       moduleObject.hot = module.hot;
     }
 
     // keep args in sync with with defineModuleCode in
     // metro-bundler/src/Resolver/index.js
     // and metro-bundler/src/ModuleGraph/worker.js
-    factory(global, require, moduleObject, exports, dependencyMap);
+    factory.call(
+      module.exports,
+      global,
+      require,
+      moduleObject,
+      module.exports,
+      dependencyMap,
+    );
 
     // avoid removing factory in DEV mode as it breaks HMR
     if (!__DEV__) {
@@ -205,7 +228,7 @@ function loadModuleImplementation(moduleId, module) {
       // $FlowFixMe: we know that __DEV__ is const and `Systrace` exists
       Systrace.endEvent();
     }
-    return (module.exports = moduleObject.exports);
+    return module.exports;
   } catch (e) {
     module.hasError = true;
     module.error = e;

packages/metro-bundler/src/integration_tests/__tests__/__snapshots__/basic_bundle-test.js.snap

@@ -83,23 +83,39 @@ function loadModuleImplementation(moduleId, module) {
   }
 
   module.isInitialized = true;
-  var exports = module.exports = {};
+  module.exports = {};
   var _module = module,
       factory = _module.factory,
       dependencyMap = _module.dependencyMap;
 
   try {
 
-    var _moduleObject = { exports: exports };
-
-    factory(global, _require, _moduleObject, exports, dependencyMap);
+      var _moduleObject = {
+      get id() {
+        return moduleId;
+      },
+      get hot() {
+        return module.hot;
+      },
+      set hot(value) {
+        module.hot = value;
+      },
+      get exports() {
+        return module.exports;
+      },
+      set exports(value) {
+        module.exports = value;
+      }
+    };
+
+    factory.call(module.exports, global, _require, _moduleObject, module.exports, dependencyMap);
 
     {
       module.factory = undefined;
       module.dependencyMap = undefined;
     }
 
-    return module.exports = _moduleObject.exports;
+    return module.exports;
   } catch (e) {
     module.hasError = true;
     module.error = e;
@@ -253,23 +269,39 @@ function loadModuleImplementation(moduleId, module) {
   }
 
   module.isInitialized = true;
-  var exports = module.exports = {};
+  module.exports = {};
   var _module = module,
       factory = _module.factory,
       dependencyMap = _module.dependencyMap;
 
   try {
 
-    var _moduleObject = { exports: exports };
-
-    factory(global, _require, _moduleObject, exports, dependencyMap);
+    var _moduleObject = {
+      get id() {
+        return moduleId;
+      },
+      get hot() {
+        return module.hot;
+      },
+      set hot(value) {
+        module.hot = value;
+      },
+      get exports() {
+        return module.exports;
+      },
+      set exports(value) {
+        module.exports = value;
+      }
+    };
+
+    factory.call(module.exports, global, _require, _moduleObject, module.exports, dependencyMap);
 
     {
       module.factory = undefined;
       module.dependencyMap = undefined;
     }
 
-    return module.exports = _moduleObject.exports;
+    return module.exports;
   } catch (e) {
     module.hasError = true;
     module.error = e;