diff --git a/.changeset/config.json b/.changeset/config.json
index af95312e25a..6791d5c6557 100644
--- a/.changeset/config.json
+++ b/.changeset/config.json
@@ -13,6 +13,7 @@
     "firebase-namespace-integration-test",
     "firebase-firestore-integration-test",
     "firebase-messaging-integration-test",
+    "firebase-compat-interop-test",
     "firebase-compat-typings-test",
     "@firebase/app-exp",
     "@firebase/analytics-compat",
diff --git a/.changeset/fuzzy-teachers-guess.md b/.changeset/fuzzy-teachers-guess.md
new file mode 100644
index 00000000000..8c67248724c
--- /dev/null
+++ b/.changeset/fuzzy-teachers-guess.md
@@ -0,0 +1,5 @@
+---
+"@firebase/component": patch
+---
+
+handle `undefined` correctly from input.
diff --git a/integration/compat-interop/analytics.test.ts b/integration/compat-interop/analytics.test.ts
new file mode 100644
index 00000000000..637e533286d
--- /dev/null
+++ b/integration/compat-interop/analytics.test.ts
@@ -0,0 +1,35 @@
+/**
+ * @license
+ * Copyright 2021 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { getModularInstance } from '@firebase/util';
+import { expect } from 'chai';
+import { getAnalytics } from '@firebase/analytics-exp';
+import firebase from '@firebase/app-compat';
+import '@firebase/analytics-compat';
+
+import { TEST_PROJECT_CONFIG } from './util';
+
+firebase.initializeApp(TEST_PROJECT_CONFIG);
+
+const compatAnalytics = firebase.analytics();
+const modularAnalytics = getAnalytics();
+
+describe('Analytics compat interop', () => {
+  it('Analytics compat instance references modular Analytics instance', () => {
+    expect(getModularInstance(compatAnalytics)).to.equal(modularAnalytics);
+  });
+});
diff --git a/integration/compat-interop/app.test.ts b/integration/compat-interop/app.test.ts
new file mode 100644
index 00000000000..4a79c4b5bc3
--- /dev/null
+++ b/integration/compat-interop/app.test.ts
@@ -0,0 +1,50 @@
+/**
+ * @license
+ * Copyright 2021 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { getModularInstance } from '@firebase/util';
+import { expect } from 'chai';
+import { getApp, getApps } from '@firebase/app-exp';
+import firebase from '@firebase/app-compat';
+
+import { TEST_PROJECT_CONFIG } from './util';
+//TODO: add Storage, Firestore and Database tests once v8 is removed. Currently it's too difficult to set them up in integration tests.
+describe('App compat interop', () => {
+  afterEach(() => {
+    const deletePromises = [];
+    for (const app of firebase.apps) {
+      deletePromises.push(app.delete());
+    }
+
+    return Promise.all(deletePromises);
+  });
+
+  it('App compat instance references modular App instance', () => {
+    const compatApp = firebase.initializeApp(TEST_PROJECT_CONFIG);
+    const modularApp = getApp();
+    expect(getModularInstance(compatApp)).to.equal(modularApp);
+  });
+
+  it('deleting compat app deletes modular app', async () => {
+    const compatApp = firebase.initializeApp(TEST_PROJECT_CONFIG);
+    expect(firebase.apps.length).to.equal(1);
+    expect(getApps().length).to.equal(1);
+
+    await compatApp.delete();
+    expect(firebase.apps.length).to.equal(0);
+    expect(getApps().length).to.equal(0);
+  });
+});
diff --git a/integration/compat-interop/auth.test.ts b/integration/compat-interop/auth.test.ts
new file mode 100644
index 00000000000..b15b368ed22
--- /dev/null
+++ b/integration/compat-interop/auth.test.ts
@@ -0,0 +1,49 @@
+/**
+ * @license
+ * Copyright 2021 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { getModularInstance } from '@firebase/util';
+import { expect } from 'chai';
+import { getAuth, signOut } from '@firebase/auth-exp';
+import firebase from '@firebase/app-compat';
+import '@firebase/auth-compat';
+
+import { TEST_PROJECT_CONFIG } from './util';
+
+firebase.initializeApp(TEST_PROJECT_CONFIG);
+
+const compatAuth = firebase.auth();
+const modularAuth = getAuth();
+
+describe('Auth compat interop', () => {
+  it('Auth compat instance references modular Auth instance', () => {
+    expect(getModularInstance(compatAuth)).to.equal(modularAuth);
+  });
+
+  it('Auth compat and modular Auth share the same user state', async () => {
+    expect(compatAuth.currentUser).to.equal(null);
+    expect(modularAuth.currentUser).to.equal(null);
+    const userCred = await compatAuth.signInAnonymously();
+    expect(userCred.user?.uid).to.equal(modularAuth.currentUser?.uid);
+    expect(await userCred.user?.getIdToken()).to.equal(
+      await modularAuth.currentUser?.getIdToken()
+    );
+
+    await signOut(modularAuth);
+    expect(compatAuth.currentUser).to.equal(null);
+    expect(modularAuth.currentUser).to.equal(null);
+  });
+});
diff --git a/integration/compat-interop/functions.test.ts b/integration/compat-interop/functions.test.ts
new file mode 100644
index 00000000000..327fd8bde94
--- /dev/null
+++ b/integration/compat-interop/functions.test.ts
@@ -0,0 +1,35 @@
+/**
+ * @license
+ * Copyright 2021 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { getModularInstance } from '@firebase/util';
+import { expect } from 'chai';
+import { getFunctions } from '@firebase/functions-exp';
+import firebase from '@firebase/app-compat';
+import '@firebase/functions-compat';
+
+import { TEST_PROJECT_CONFIG } from './util';
+
+firebase.initializeApp(TEST_PROJECT_CONFIG);
+
+const compatFunction = firebase.functions();
+const modularFunctions = getFunctions();
+
+describe('Functions compat interop', () => {
+  it('Functions compat instance references modular Functions instance', () => {
+    expect(getModularInstance(compatFunction)).to.equal(modularFunctions);
+  });
+});
diff --git a/integration/compat-interop/karma.conf.js b/integration/compat-interop/karma.conf.js
new file mode 100644
index 00000000000..6dde3b61344
--- /dev/null
+++ b/integration/compat-interop/karma.conf.js
@@ -0,0 +1,36 @@
+/**
+ * @license
+ * Copyright 2017 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+const karma = require('karma');
+const karmaBase = require('../../config/karma.base');
+
+const files = ['*.test.*'];
+
+module.exports = function (config) {
+  const karmaConfig = Object.assign({}, karmaBase, {
+    // files to load into karma
+    files: files,
+    preprocessors: { '**/*.ts': ['webpack', 'sourcemap'] },
+    // frameworks to use
+    // available frameworks: https://npmjs.org/browse/keyword/karma-adapter
+    frameworks: ['mocha']
+  });
+
+  config.set(karmaConfig);
+};
+
+module.exports.files = files;
diff --git a/integration/compat-interop/messaging.test.ts b/integration/compat-interop/messaging.test.ts
new file mode 100644
index 00000000000..88758d2e3e3
--- /dev/null
+++ b/integration/compat-interop/messaging.test.ts
@@ -0,0 +1,35 @@
+/**
+ * @license
+ * Copyright 2021 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { getModularInstance } from '@firebase/util';
+import { expect } from 'chai';
+import { getMessaging } from '@firebase/messaging-exp';
+import firebase from '@firebase/app-compat';
+import '@firebase/messaging-compat';
+
+import { TEST_PROJECT_CONFIG } from './util';
+
+firebase.initializeApp(TEST_PROJECT_CONFIG);
+
+const compatMessaging = firebase.messaging();
+const modularMessaging = getMessaging();
+
+describe('Messaging compat interop', () => {
+  it('Messaging compat instance references modular Messaging instance', () => {
+    expect(getModularInstance(compatMessaging)).to.equal(modularMessaging);
+  });
+});
diff --git a/integration/compat-interop/package.json b/integration/compat-interop/package.json
new file mode 100644
index 00000000000..f47062301c4
--- /dev/null
+++ b/integration/compat-interop/package.json
@@ -0,0 +1,29 @@
+{
+    "name": "firebase-compat-interop-test",
+    "private": true,
+    "version": "0.1.0",
+    "scripts": {
+        "test": "karma start --single-run",
+        "test:ci": "node ../../scripts/run_tests_in_ci.js -s test",
+        "test:debug": "karma start --browsers Chrome --auto-watch"
+    },
+    "dependencies": {
+      "@firebase/app-exp": "0.0.900",
+      "@firebase/app-compat": "0.0.900",
+      "@firebase/analytics-exp": "0.0.900",
+      "@firebase/analytics-compat": "0.0.900",
+      "@firebase/auth-exp": "0.0.900",
+      "@firebase/auth-compat": "0.0.900",
+      "@firebase/functions-exp": "0.0.900",
+      "@firebase/functions-compat": "0.0.900",
+      "@firebase/messaging-exp": "0.0.900",
+      "@firebase/messaging-compat": "0.0.900",
+      "@firebase/performance-exp": "0.0.900",
+      "@firebase/performance-compat": "0.0.900",
+      "@firebase/remote-config-exp": "0.0.900",
+      "@firebase/remote-config-compat": "0.0.900"
+    },
+    "devDependencies": {
+      "typescript": "4.2.2"
+    }
+  }
\ No newline at end of file
diff --git a/integration/compat-interop/performance.test.ts b/integration/compat-interop/performance.test.ts
new file mode 100644
index 00000000000..6820b0cb368
--- /dev/null
+++ b/integration/compat-interop/performance.test.ts
@@ -0,0 +1,60 @@
+/**
+ * @license
+ * Copyright 2021 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { getModularInstance } from '@firebase/util';
+import { expect } from 'chai';
+import { getPerformance } from '@firebase/performance-exp';
+import firebase from '@firebase/app-compat';
+import '@firebase/performance-compat';
+
+import { TEST_PROJECT_CONFIG } from './util';
+
+firebase.initializeApp(TEST_PROJECT_CONFIG);
+
+const compatPerf = firebase.performance();
+const modularPerf = getPerformance();
+
+describe('Performance compat interop', () => {
+  it('Performance compat instance references modular Performance instance', () => {
+    expect(getModularInstance(compatPerf)).to.equal(modularPerf);
+  });
+
+  it('Performance compat and modular Performance instance share the same configuration', () => {
+    expect(compatPerf.dataCollectionEnabled).to.equal(true);
+    expect(compatPerf.instrumentationEnabled).to.equal(true);
+    expect(modularPerf.dataCollectionEnabled).to.equal(true);
+    expect(modularPerf.instrumentationEnabled).to.equal(true);
+
+    // change settings on the compat instance
+    compatPerf.dataCollectionEnabled = false;
+    compatPerf.instrumentationEnabled = false;
+
+    expect(compatPerf.dataCollectionEnabled).to.equal(false);
+    expect(compatPerf.instrumentationEnabled).to.equal(false);
+    expect(modularPerf.dataCollectionEnabled).to.equal(false);
+    expect(modularPerf.instrumentationEnabled).to.equal(false);
+
+    // change settings on the modular instance
+    modularPerf.dataCollectionEnabled = true;
+    modularPerf.instrumentationEnabled = true;
+
+    expect(compatPerf.dataCollectionEnabled).to.equal(true);
+    expect(compatPerf.instrumentationEnabled).to.equal(true);
+    expect(modularPerf.dataCollectionEnabled).to.equal(true);
+    expect(modularPerf.instrumentationEnabled).to.equal(true);
+  });
+});
diff --git a/integration/compat-interop/remote-config.test.ts b/integration/compat-interop/remote-config.test.ts
new file mode 100644
index 00000000000..580832aee12
--- /dev/null
+++ b/integration/compat-interop/remote-config.test.ts
@@ -0,0 +1,35 @@
+/**
+ * @license
+ * Copyright 2021 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { getModularInstance } from '@firebase/util';
+import { expect } from 'chai';
+import { getRemoteConfig } from '@firebase/remote-config-exp';
+import firebase from '@firebase/app-compat';
+import '@firebase/remote-config-compat';
+
+import { TEST_PROJECT_CONFIG } from './util';
+
+firebase.initializeApp(TEST_PROJECT_CONFIG);
+
+const compatRC = firebase.remoteConfig();
+const modularRC = getRemoteConfig();
+
+describe('RC compat interop', () => {
+  it('RC compat instance references modular RC instance', () => {
+    expect(getModularInstance(compatRC)).to.equal(modularRC);
+  });
+});
diff --git a/integration/compat-interop/tsconfig.json b/integration/compat-interop/tsconfig.json
new file mode 100644
index 00000000000..4da78214594
--- /dev/null
+++ b/integration/compat-interop/tsconfig.json
@@ -0,0 +1,19 @@
+{
+  "extends": "../../config/tsconfig.base.json",
+  "compileOnSave": false,
+  "compilerOptions": {
+    "allowJs": true,
+    "declaration": false,
+    "module": "commonjs",
+    "moduleResolution": "node",
+    "noImplicitAny": true,
+    "outDir": "dist",
+    "target": "ES5",
+    "sourceMap": true,
+    "esModuleInterop": true
+  },
+  "exclude": [
+    "node_modules",
+    "dist"
+  ]
+}
diff --git a/integration/compat-interop/util.ts b/integration/compat-interop/util.ts
new file mode 100644
index 00000000000..68734591c6e
--- /dev/null
+++ b/integration/compat-interop/util.ts
@@ -0,0 +1,18 @@
+/**
+ * @license
+ * Copyright 2021 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+export const TEST_PROJECT_CONFIG = require('../../config/project.json');
diff --git a/packages-exp/functions-compat/src/index.ts b/packages-exp/functions-compat/src/index.ts
index 8be24bbe6d4..ac85ad18dce 100644
--- a/packages-exp/functions-compat/src/index.ts
+++ b/packages-exp/functions-compat/src/index.ts
@@ -25,12 +25,12 @@ firebase.registerVersion(name, version);
 
 declare module '@firebase/app-compat' {
   interface FirebaseNamespace {
-    functions?: {
+    functions: {
       (app?: FirebaseApp): types.FirebaseFunctions;
       Functions: typeof types.FirebaseFunctions;
     };
   }
   interface FirebaseApp {
-    functions?(regionOrCustomDomain?: string): types.FirebaseFunctions;
+    functions(regionOrCustomDomain?: string): types.FirebaseFunctions;
   }
 }
diff --git a/packages-exp/performance-compat/src/index.ts b/packages-exp/performance-compat/src/index.ts
index 7fed7ca8c8b..0a2109ee3f0 100644
--- a/packages-exp/performance-compat/src/index.ts
+++ b/packages-exp/performance-compat/src/index.ts
@@ -58,11 +58,11 @@ registerPerformanceCompat(firebase as _FirebaseNamespace);
 
 declare module '@firebase/app-compat' {
   interface FirebaseNamespace {
-    performance?: {
+    performance: {
       (app?: FirebaseApp): FirebasePerformanceCompat;
     };
   }
   interface FirebaseApp {
-    performance?(): FirebasePerformanceCompat;
+    performance(): FirebasePerformanceCompat;
   }
 }
diff --git a/packages-exp/remote-config-compat/src/index.ts b/packages-exp/remote-config-compat/src/index.ts
index 11c472c7ead..88de17406cf 100644
--- a/packages-exp/remote-config-compat/src/index.ts
+++ b/packages-exp/remote-config-compat/src/index.ts
@@ -64,7 +64,7 @@ registerRemoteConfigCompat(firebase as _FirebaseNamespace);
 
 declare module '@firebase/app-compat' {
   interface FirebaseNamespace {
-    remoteConfig?: {
+    remoteConfig: {
       (app?: FirebaseApp): RemoteConfigCompat;
     };
   }
diff --git a/packages/component/src/provider.ts b/packages/component/src/provider.ts
index d5a171b6c3a..de01e815691 100644
--- a/packages/component/src/provider.ts
+++ b/packages/component/src/provider.ts
@@ -99,11 +99,9 @@ export class Provider<T extends Name> {
     identifier?: string;
     optional?: boolean;
   }): NameServiceMapping[T] | null {
-    const { identifier, optional } = {
-      identifier: DEFAULT_ENTRY_NAME,
-      optional: false,
-      ...options
-    };
+    const identifier = options?.identifier ?? DEFAULT_ENTRY_NAME;
+    const optional = options?.optional ?? false;
+
     // if multipleInstances is not supported, use the default name
     const normalizedIdentifier = this.normalizeInstanceIdentifier(identifier);
 
diff --git a/yarn.lock b/yarn.lock
index 174872ed50a..5c652bc7122 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -2557,6 +2557,13 @@
   dependencies:
     "@types/glob" "*"
 
+"@types/archiver@^5.1.0":
+  version "5.1.0"
+  resolved "https://registry.npmjs.org/@types/archiver/-/archiver-5.1.0.tgz#869f4ce4028e49cf9a0243cf914415f4cc3d1f3d"
+  integrity sha512-baFOhanb/hxmcOd1Uey2TfFg43kTSmM6py1Eo7Rjbv/ivcl7PXLhY0QgXGf50Hx/eskGCFqPfhs/7IZLb15C5g==
+  dependencies:
+    "@types/glob" "*"
+
 "@types/argparse@1.0.38":
   version "1.0.38"
   resolved "https://registry.npmjs.org/@types/argparse/-/argparse-1.0.38.tgz#a81fd8606d481f873a3800c6ebae4f1d768a56a9"
@@ -8328,6 +8335,18 @@ get-uri@3:
     fs-extra "^8.1.0"
     ftp "^0.3.10"
 
+get-uri@3:
+  version "3.0.2"
+  resolved "https://registry.npmjs.org/get-uri/-/get-uri-3.0.2.tgz#f0ef1356faabc70e1f9404fa3b66b2ba9bfc725c"
+  integrity sha512-+5s0SJbGoyiJTZZ2JTpFPLMPSch72KEqGOTvQsBqg0RBWvwhWUSYZFAtz3TPW0GXJuLBJPts1E241iHg+VRfhg==
+  dependencies:
+    "@tootallnate/once" "1"
+    data-uri-to-buffer "3"
+    debug "4"
+    file-uri-to-path "2"
+    fs-extra "^8.1.0"
+    ftp "^0.3.10"
+
 get-value@^2.0.3, get-value@^2.0.6:
   version "2.0.6"
   resolved "https://registry.npmjs.org/get-value/-/get-value-2.0.6.tgz#dc15ca1c672387ca76bd37ac0a395ba2042a2c28"
@@ -16428,6 +16447,11 @@ tslib@^2.0.1, tslib@^2.1.0, tslib@^2.2.0:
   resolved "https://registry.npmjs.org/tslib/-/tslib-2.2.0.tgz#fb2c475977e35e241311ede2693cee1ec6698f5c"
   integrity sha512-gS9GVHRU+RGn5KQM2rllAlR3dU6m7AcpJKdtH8gFvQiC4Otgk98XnmMU+nZenHt/+VhnBPWwgrJsyrdcw6i23w==
 
+tslib@^2.0.1:
+  version "2.2.0"
+  resolved "https://registry.npmjs.org/tslib/-/tslib-2.2.0.tgz#fb2c475977e35e241311ede2693cee1ec6698f5c"
+  integrity sha512-gS9GVHRU+RGn5KQM2rllAlR3dU6m7AcpJKdtH8gFvQiC4Otgk98XnmMU+nZenHt/+VhnBPWwgrJsyrdcw6i23w==
+
 tslint@6.1.3:
   version "6.1.3"
   resolved "https://registry.npmjs.org/tslint/-/tslint-6.1.3.tgz#5c23b2eccc32487d5523bd3a470e9aa31789d904"