diff --git a/packages/compiler-cli/ngcc/src/main.ts b/packages/compiler-cli/ngcc/src/main.ts
index 4fb88c1e18..b359b9af5b 100644
--- a/packages/compiler-cli/ngcc/src/main.ts
+++ b/packages/compiler-cli/ngcc/src/main.ts
@@ -20,6 +20,7 @@ import {EntryPointFinder} from './packages/entry_point_finder';
 import {Transformer} from './packages/transformer';
 import {FileWriter} from './writing/file_writer';
 import {InPlaceFileWriter} from './writing/in_place_file_writer';
+import {NewEntryPointFileWriter} from './writing/new_entry_point_file_writer';
 
 
 /**
@@ -45,6 +46,10 @@ export interface NgccOptions {
    * this entry-point at the first matching format. Defaults to `true`.
    */
   compileAllFormats?: boolean;
+  /**
+   * Whether to create new entry-points bundles rather than overwriting the original files.
+   */
+  createNewEntryPointFormats?: boolean;
 }
 
 const SUPPORTED_FORMATS: EntryPointFormat[] = ['esm5', 'esm2015'];
@@ -57,14 +62,14 @@ const SUPPORTED_FORMATS: EntryPointFormat[] = ['esm5', 'esm2015'];
  *
  * @param options The options telling ngcc what to compile and how.
  */
-export function mainNgcc({basePath, targetEntryPointPath,
-                          propertiesToConsider = SUPPORTED_FORMAT_PROPERTIES,
-                          compileAllFormats = true}: NgccOptions): void {
+export function mainNgcc(
+    {basePath, targetEntryPointPath, propertiesToConsider = SUPPORTED_FORMAT_PROPERTIES,
+     compileAllFormats = true, createNewEntryPointFormats = false}: NgccOptions): void {
   const transformer = new Transformer(basePath, basePath);
   const host = new DependencyHost();
   const resolver = new DependencyResolver(host);
   const finder = new EntryPointFinder(resolver);
-  const fileWriter = getFileWriter();
+  const fileWriter = getFileWriter(createNewEntryPointFormats);
 
   const absoluteTargetEntryPointPath = targetEntryPointPath ?
       AbsoluteFsPath.from(resolve(basePath, targetEntryPointPath)) :
@@ -115,7 +120,7 @@ export function mainNgcc({basePath, targetEntryPointPath,
       // the property as processed even if its underlying format has been built already.
       if (!compiledFormats.has(formatPath) && (compileAllFormats || compiledFormats.size === 0)) {
         const bundle = makeEntryPointBundle(
-            entryPoint.path, formatPath, entryPoint.typings, isCore, format,
+            entryPoint.path, formatPath, entryPoint.typings, isCore, property, format,
             compiledFormats.size === 0);
         if (bundle) {
           console.warn(`Compiling ${entryPoint.name} : ${property} as ${format}`);
@@ -144,6 +149,6 @@ export function mainNgcc({basePath, targetEntryPointPath,
   });
 }
 
-function getFileWriter(): FileWriter {
-  return new InPlaceFileWriter();
+function getFileWriter(createNewEntryPointFormats: boolean): FileWriter {
+  return createNewEntryPointFormats ? new NewEntryPointFileWriter() : new InPlaceFileWriter();
 }
diff --git a/packages/compiler-cli/ngcc/src/packages/entry_point_bundle.ts b/packages/compiler-cli/ngcc/src/packages/entry_point_bundle.ts
index a911b39909..0130d52677 100644
--- a/packages/compiler-cli/ngcc/src/packages/entry_point_bundle.ts
+++ b/packages/compiler-cli/ngcc/src/packages/entry_point_bundle.ts
@@ -10,7 +10,7 @@ import * as ts from 'typescript';
 
 import {AbsoluteFsPath} from '../../../src/ngtsc/path';
 import {BundleProgram, makeBundleProgram} from './bundle_program';
-import {EntryPointFormat} from './entry_point';
+import {EntryPointFormat, EntryPointJsonProperty} from './entry_point';
 
 
 
@@ -19,6 +19,7 @@ import {EntryPointFormat} from './entry_point';
  * format of a package entry-point.
  */
 export interface EntryPointBundle {
+  formatProperty: EntryPointJsonProperty;
   format: EntryPointFormat;
   isCore: boolean;
   isFlatCore: boolean;
@@ -38,7 +39,8 @@ export interface EntryPointBundle {
  */
 export function makeEntryPointBundle(
     entryPointPath: string, formatPath: string, typingsPath: string, isCore: boolean,
-    format: EntryPointFormat, transformDts: boolean): EntryPointBundle|null {
+    formatProperty: EntryPointJsonProperty, format: EntryPointFormat,
+    transformDts: boolean): EntryPointBundle|null {
   // Create the TS program and necessary helpers.
   const options: ts.CompilerOptions = {
     allowJs: true,
@@ -57,5 +59,5 @@ export function makeEntryPointBundle(
       null;
   const isFlatCore = isCore && src.r3SymbolsFile === null;
 
-  return {format, rootDirs, isCore, isFlatCore, src, dts};
+  return {format, formatProperty, rootDirs, isCore, isFlatCore, src, dts};
 }
diff --git a/packages/compiler-cli/ngcc/src/writing/new_entry_point_file_writer.ts b/packages/compiler-cli/ngcc/src/writing/new_entry_point_file_writer.ts
new file mode 100644
index 0000000000..b79e4ed174
--- /dev/null
+++ b/packages/compiler-cli/ngcc/src/writing/new_entry_point_file_writer.ts
@@ -0,0 +1,72 @@
+
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {dirname, join, relative} from 'canonical-path';
+import {writeFileSync} from 'fs';
+import {cp, mkdir} from 'shelljs';
+
+import {AbsoluteFsPath} from '../../../src/ngtsc/path';
+import {isDtsPath} from '../../../src/ngtsc/util/src/typescript';
+import {EntryPoint, EntryPointJsonProperty} from '../packages/entry_point';
+import {EntryPointBundle} from '../packages/entry_point_bundle';
+import {FileInfo} from '../rendering/renderer';
+
+import {InPlaceFileWriter} from './in_place_file_writer';
+
+const NGCC_DIRECTORY = '__ivy_ngcc__';
+
+/**
+ * This FileWriter creates a copy of the original entry-point, then writes the transformed
+ * files onto the files in this copy, and finally updates the package.json with a new
+ * entry-point format property that points to this new entry-point.
+ *
+ * If there are transformed typings files in this bundle, they are updated in-place (see the
+ * `InPlaceFileWriter`).
+ */
+export class NewEntryPointFileWriter extends InPlaceFileWriter {
+  writeBundle(entryPoint: EntryPoint, bundle: EntryPointBundle, transformedFiles: FileInfo[]) {
+    // The new folder is at the root of the overall package
+    const relativeEntryPointPath = relative(entryPoint.package, entryPoint.path);
+    const relativeNewDir = join(NGCC_DIRECTORY, relativeEntryPointPath);
+    const newDir = AbsoluteFsPath.fromUnchecked(join(entryPoint.package, relativeNewDir));
+    this.copyBundle(bundle, entryPoint.path, newDir);
+    transformedFiles.forEach(file => this.writeFile(file, entryPoint.path, newDir));
+    this.updatePackageJson(entryPoint, bundle.formatProperty, newDir);
+  }
+
+  protected copyBundle(
+      bundle: EntryPointBundle, entryPointPath: AbsoluteFsPath, newDir: AbsoluteFsPath) {
+    bundle.src.program.getSourceFiles().forEach(sourceFile => {
+      const relativePath = relative(entryPointPath, sourceFile.fileName);
+      const newFilePath = join(newDir, relativePath);
+      mkdir('-p', dirname(newFilePath));
+      cp(sourceFile.fileName, newFilePath);
+    });
+  }
+
+  protected writeFile(file: FileInfo, entryPointPath: AbsoluteFsPath, newDir: AbsoluteFsPath):
+      void {
+    if (isDtsPath(file.path)) {
+      super.writeFileAndBackup(file);
+    } else {
+      const relativePath = relative(entryPointPath, file.path);
+      const newFilePath = join(newDir, relativePath);
+      mkdir('-p', dirname(newFilePath));
+      writeFileSync(newFilePath, file.contents, 'utf8');
+    }
+  }
+
+  protected updatePackageJson(
+      entryPoint: EntryPoint, formatProperty: EntryPointJsonProperty, newDir: AbsoluteFsPath) {
+    const bundlePath = entryPoint.packageJson[formatProperty] !;
+    const newBundlePath = relative(entryPoint.path, join(newDir, bundlePath));
+    (entryPoint.packageJson as any)[formatProperty + '_ivy_ngcc'] = newBundlePath;
+    writeFileSync(join(entryPoint.path, 'package.json'), JSON.stringify(entryPoint.packageJson));
+  }
+}
diff --git a/packages/compiler-cli/ngcc/test/helpers/utils.ts b/packages/compiler-cli/ngcc/test/helpers/utils.ts
index 4e06fe32dd..6969c51ea5 100644
--- a/packages/compiler-cli/ngcc/test/helpers/utils.ts
+++ b/packages/compiler-cli/ngcc/test/helpers/utils.ts
@@ -10,7 +10,7 @@ import * as ts from 'typescript';
 import {AbsoluteFsPath} from '../../../src/ngtsc/path';
 import {makeProgram} from '../../../src/ngtsc/testing/in_memory_typescript';
 import {BundleProgram} from '../../src/packages/bundle_program';
-import {EntryPointFormat} from '../../src/packages/entry_point';
+import {EntryPointFormat, EntryPointJsonProperty} from '../../src/packages/entry_point';
 import {EntryPointBundle} from '../../src/packages/entry_point_bundle';
 
 export {getDeclaration} from '../../../src/ngtsc/testing/in_memory_typescript';
@@ -22,13 +22,17 @@ export {getDeclaration} from '../../../src/ngtsc/testing/in_memory_typescript';
  * @param dtsFiles The typings files to include the bundle.
  */
 export function makeTestEntryPointBundle(
-    format: EntryPointFormat, isCore: boolean,
+    formatProperty: EntryPointJsonProperty, format: EntryPointFormat, isCore: boolean,
     files: {name: string, contents: string, isRoot?: boolean}[],
     dtsFiles?: {name: string, contents: string, isRoot?: boolean}[]): EntryPointBundle {
   const src = makeTestBundleProgram(files);
   const dts = dtsFiles ? makeTestBundleProgram(dtsFiles) : null;
   const isFlatCore = isCore && src.r3SymbolsFile === null;
-  return {format, rootDirs: [AbsoluteFsPath.fromUnchecked('/')], src, dts, isCore, isFlatCore};
+  return {
+    formatProperty,
+    format,
+    rootDirs: [AbsoluteFsPath.fromUnchecked('/')], src, dts, isCore, isFlatCore
+  };
 }
 
 /**
diff --git a/packages/compiler-cli/ngcc/test/integration/ngcc_spec.ts b/packages/compiler-cli/ngcc/test/integration/ngcc_spec.ts
index adc91151fc..3c2593d7d7 100644
--- a/packages/compiler-cli/ngcc/test/integration/ngcc_spec.ts
+++ b/packages/compiler-cli/ngcc/test/integration/ngcc_spec.ts
@@ -141,6 +141,44 @@ describe('ngcc main()', () => {
       });
     });
   });
+
+  describe('with createNewEntryPointFormats', () => {
+    it('should create new files rather than overwriting the originals', () => {
+      const ANGULAR_CORE_IMPORT_REGEX = /import \* as ɵngcc\d+ from '@angular\/core';/;
+      mainNgcc({
+        basePath: '/node_modules',
+        createNewEntryPointFormats: true,
+        propertiesToConsider: ['esm5']
+      });
+
+      // Updates the package.json
+      expect(loadPackage('@angular/common').esm5).toEqual('./esm5/common.js');
+      expect((loadPackage('@angular/common') as any).esm5_ivy_ngcc)
+          .toEqual('__ivy_ngcc__/esm5/common.js');
+
+      // Doesn't touch original files
+      expect(readFileSync(`/node_modules/@angular/common/esm5/src/common_module.js`, 'utf8'))
+          .not.toMatch(ANGULAR_CORE_IMPORT_REGEX);
+      // Or create a backup of the original
+      expect(existsSync(`/node_modules/@angular/common/esm5/src/common_module.js.__ivy_ngcc_bak`))
+          .toBe(false);
+
+      // Creates new files
+      expect(readFileSync(
+                 `/node_modules/@angular/common/__ivy_ngcc__/esm5/src/common_module.js`, 'utf8'))
+          .toMatch(ANGULAR_CORE_IMPORT_REGEX);
+
+      // Copies over files (unchanged) that did not need compiling
+      expect(existsSync(`/node_modules/@angular/common/__ivy_ngcc__/esm5/src/version.js`));
+      expect(readFileSync(`/node_modules/@angular/common/__ivy_ngcc__/esm5/src/version.js`, 'utf8'))
+          .toEqual(readFileSync(`/node_modules/@angular/common/esm5/src/version.js`, 'utf8'));
+
+      // Overwrites .d.ts files (as usual)
+      expect(readFileSync(`/node_modules/@angular/common/common.d.ts`, 'utf8'))
+          .toMatch(ANGULAR_CORE_IMPORT_REGEX);
+      expect(existsSync(`/node_modules/@angular/common/common.d.ts.__ivy_ngcc_bak`)).toBe(true);
+    });
+  });
 });
 
 
@@ -232,4 +270,4 @@ function mockResolve(request: string): string|null {
 
 function loadPackage(packageName: string): EntryPointPackageJson {
   return JSON.parse(readFileSync(`/node_modules/${packageName}/package.json`, 'utf8'));
-}
\ No newline at end of file
+}
diff --git a/packages/compiler-cli/ngcc/test/rendering/esm2015_renderer_spec.ts b/packages/compiler-cli/ngcc/test/rendering/esm2015_renderer_spec.ts
index 52c35f6af0..9176141ae1 100644
--- a/packages/compiler-cli/ngcc/test/rendering/esm2015_renderer_spec.ts
+++ b/packages/compiler-cli/ngcc/test/rendering/esm2015_renderer_spec.ts
@@ -18,7 +18,7 @@ import {makeTestEntryPointBundle} from '../helpers/utils';
 
 function setup(file: {name: string, contents: string}) {
   const dir = dirname(file.name);
-  const bundle = makeTestEntryPointBundle('esm2015', false, [file]) !;
+  const bundle = makeTestEntryPointBundle('es2015', 'esm2015', false, [file]) !;
   const typeChecker = bundle.src.program.getTypeChecker();
   const host = new Esm2015ReflectionHost(false, typeChecker);
   const referencesRegistry = new NgccReferencesRegistry(host);
diff --git a/packages/compiler-cli/ngcc/test/rendering/esm5_renderer_spec.ts b/packages/compiler-cli/ngcc/test/rendering/esm5_renderer_spec.ts
index b87ef4e3f9..efb1641690 100644
--- a/packages/compiler-cli/ngcc/test/rendering/esm5_renderer_spec.ts
+++ b/packages/compiler-cli/ngcc/test/rendering/esm5_renderer_spec.ts
@@ -18,7 +18,7 @@ import {makeTestEntryPointBundle, getDeclaration} from '../helpers/utils';
 
 function setup(file: {name: string, contents: string}) {
   const dir = dirname(file.name);
-  const bundle = makeTestEntryPointBundle('esm5', false, [file]);
+  const bundle = makeTestEntryPointBundle('module', 'esm5', false, [file]);
   const typeChecker = bundle.src.program.getTypeChecker();
   const host = new Esm5ReflectionHost(false, typeChecker);
   const referencesRegistry = new NgccReferencesRegistry(host);
diff --git a/packages/compiler-cli/ngcc/test/rendering/renderer_spec.ts b/packages/compiler-cli/ngcc/test/rendering/renderer_spec.ts
index dd68f21e6f..775068bd4c 100644
--- a/packages/compiler-cli/ngcc/test/rendering/renderer_spec.ts
+++ b/packages/compiler-cli/ngcc/test/rendering/renderer_spec.ts
@@ -50,7 +50,7 @@ function createTestRenderer(
     packageName: string, files: {name: string, contents: string}[],
     dtsFiles?: {name: string, contents: string}[]) {
   const isCore = packageName === '@angular/core';
-  const bundle = makeTestEntryPointBundle('esm2015', isCore, files, dtsFiles);
+  const bundle = makeTestEntryPointBundle('es2015', 'esm2015', isCore, files, dtsFiles);
   const typeChecker = bundle.src.program.getTypeChecker();
   const host = new Esm2015ReflectionHost(isCore, typeChecker, bundle.dts);
   const referencesRegistry = new NgccReferencesRegistry(host);
diff --git a/packages/compiler-cli/ngcc/test/writing/new_entry_point_file_writer_spec.ts b/packages/compiler-cli/ngcc/test/writing/new_entry_point_file_writer_spec.ts
new file mode 100644
index 0000000000..956fba49f0
--- /dev/null
+++ b/packages/compiler-cli/ngcc/test/writing/new_entry_point_file_writer_spec.ts
@@ -0,0 +1,282 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {existsSync, readFileSync} from 'fs';
+import * as mockFs from 'mock-fs';
+
+import {AbsoluteFsPath} from '../../../src/ngtsc/path';
+import {EntryPoint, EntryPointFormat, EntryPointJsonProperty, getEntryPointInfo} from '../../src/packages/entry_point';
+import {EntryPointBundle, makeEntryPointBundle} from '../../src/packages/entry_point_bundle';
+import {FileWriter} from '../../src/writing/file_writer';
+import {NewEntryPointFileWriter} from '../../src/writing/new_entry_point_file_writer';
+import {loadPackageJson} from '../packages/entry_point_spec';
+
+const _ = AbsoluteFsPath.from;
+
+function createMockFileSystem() {
+  mockFs({
+    '/node_modules/test': {
+      'package.json':
+          '{"module": "./esm5.js", "es2015": "./es2015/index.js", "typings": "./index.d.ts"}',
+      'index.d.ts': 'export declare class FooTop {}',
+      'index.metadata.json': '...',
+      'esm5.js': 'export function FooTop() {}',
+      'es2015': {
+        'index.js': 'import {FooTop} from "./foo";',
+        'foo.js': 'export class FooTop {}',
+      },
+      'a': {
+        'package.json':
+            '{"module": "./esm5.js", "es2015": "./es2015/index.js", "typings": "./index.d.ts"}',
+        'index.d.ts': 'export declare class FooA {}',
+        'index.metadata.json': '...',
+        'esm5.js': 'export function FooA() {}',
+        'es2015': {
+          'index.js': 'import {FooA} from "./foo";',
+          'foo.js': 'export class FooA {}',
+        },
+      },
+      'b': {
+        // This entry-point points to files outside its folder
+        'package.json':
+            '{"module": "../lib/esm5.js", "es2015": "../lib/es2015/index.js", "typings": "../typings/index.d.ts"}',
+      },
+      'lib': {
+        'esm5.js': 'export function FooB() {}',
+        'es2015': {
+          'index.js': 'import {FooB} from "./foo";',
+          'foo.js': 'export class FooB {}',
+        },
+      },
+      'typings': {
+        'index.d.ts': 'export declare class FooB {}',
+        'index.metadata.json': '...',
+      }
+    },
+  });
+}
+
+function restoreRealFileSystem() {
+  mockFs.restore();
+}
+
+describe('NewEntryPointFileWriter', () => {
+  beforeEach(createMockFileSystem);
+  afterEach(restoreRealFileSystem);
+
+  let fileWriter: FileWriter;
+  let entryPoint: EntryPoint;
+  let esm5bundle: EntryPointBundle;
+  let esm2015bundle: EntryPointBundle;
+
+  describe('writeBundle() [primary entry-point]', () => {
+    beforeEach(() => {
+      fileWriter = new NewEntryPointFileWriter();
+      entryPoint = getEntryPointInfo(_('/node_modules/test'), _('/node_modules/test')) !;
+      esm5bundle = makeTestBundle(entryPoint, 'module', 'esm5');
+      esm2015bundle = makeTestBundle(entryPoint, 'es2015', 'esm2015');
+    });
+
+    it('should write the modified file to a new folder', () => {
+      fileWriter.writeBundle(entryPoint, esm5bundle, [
+        {path: '/node_modules/test/esm5.js', contents: 'export function FooTop() {} // MODIFIED'},
+      ]);
+      expect(readFileSync('/node_modules/test/__ivy_ngcc__/esm5.js', 'utf8'))
+          .toEqual('export function FooTop() {} // MODIFIED');
+      expect(readFileSync('/node_modules/test/esm5.js', 'utf8'))
+          .toEqual('export function FooTop() {}');
+    });
+
+    it('should also copy unmodified files in the program', () => {
+      fileWriter.writeBundle(entryPoint, esm2015bundle, [
+        {path: '/node_modules/test/es2015/foo.js', contents: 'export class FooTop {} // MODIFIED'},
+      ]);
+      expect(readFileSync('/node_modules/test/__ivy_ngcc__/es2015/foo.js', 'utf8'))
+          .toEqual('export class FooTop {} // MODIFIED');
+      expect(readFileSync('/node_modules/test/es2015/foo.js', 'utf8'))
+          .toEqual('export class FooTop {}');
+      expect(readFileSync('/node_modules/test/__ivy_ngcc__/es2015/index.js', 'utf8'))
+          .toEqual('import {FooTop} from "./foo";');
+      expect(readFileSync('/node_modules/test/es2015/index.js', 'utf8'))
+          .toEqual('import {FooTop} from "./foo";');
+    });
+
+    it('should update the package.json properties', () => {
+      fileWriter.writeBundle(entryPoint, esm5bundle, [
+        {path: '/node_modules/test/esm5.js', contents: 'export function FooTop() {} // MODIFIED'},
+      ]);
+      expect(loadPackageJson('/node_modules/test')).toEqual(jasmine.objectContaining({
+        module_ivy_ngcc: '__ivy_ngcc__/esm5.js',
+      }));
+
+      fileWriter.writeBundle(entryPoint, esm2015bundle, [
+        {path: '/node_modules/test/es2015/foo.js', contents: 'export class FooTop {} // MODIFIED'},
+      ]);
+      expect(loadPackageJson('/node_modules/test')).toEqual(jasmine.objectContaining({
+        module_ivy_ngcc: '__ivy_ngcc__/esm5.js',
+        es2015_ivy_ngcc: '__ivy_ngcc__/es2015/index.js',
+      }));
+    });
+
+    it('should overwrite and backup typings files', () => {
+      fileWriter.writeBundle(entryPoint, esm2015bundle, [
+        {
+          path: '/node_modules/test/index.d.ts',
+          contents: 'export declare class FooTop {} // MODIFIED'
+        },
+      ]);
+      expect(readFileSync('/node_modules/test/index.d.ts', 'utf8'))
+          .toEqual('export declare class FooTop {} // MODIFIED');
+      expect(readFileSync('/node_modules/test/index.d.ts.__ivy_ngcc_bak', 'utf8'))
+          .toEqual('export declare class FooTop {}');
+      expect(existsSync('/node_modules/test/__ivy_ngcc__/index.d.ts')).toBe(false);
+    });
+  });
+
+  describe('writeBundle() [secondary entry-point]', () => {
+    beforeEach(() => {
+      fileWriter = new NewEntryPointFileWriter();
+      entryPoint = getEntryPointInfo(_('/node_modules/test'), _('/node_modules/test/a')) !;
+      esm5bundle = makeTestBundle(entryPoint, 'module', 'esm5');
+      esm2015bundle = makeTestBundle(entryPoint, 'es2015', 'esm2015');
+    });
+
+    it('should write the modified file to a new folder', () => {
+      fileWriter.writeBundle(entryPoint, esm5bundle, [
+        {path: '/node_modules/test/a/esm5.js', contents: 'export function FooA() {} // MODIFIED'},
+      ]);
+      expect(readFileSync('/node_modules/test/__ivy_ngcc__/a/esm5.js', 'utf8'))
+          .toEqual('export function FooA() {} // MODIFIED');
+      expect(readFileSync('/node_modules/test/a/esm5.js', 'utf8'))
+          .toEqual('export function FooA() {}');
+    });
+
+    it('should also copy unmodified files in the program', () => {
+      fileWriter.writeBundle(entryPoint, esm2015bundle, [
+        {path: '/node_modules/test/a/es2015/foo.js', contents: 'export class FooA {} // MODIFIED'},
+      ]);
+      expect(readFileSync('/node_modules/test/__ivy_ngcc__/a/es2015/foo.js', 'utf8'))
+          .toEqual('export class FooA {} // MODIFIED');
+      expect(readFileSync('/node_modules/test/a/es2015/foo.js', 'utf8'))
+          .toEqual('export class FooA {}');
+      expect(readFileSync('/node_modules/test/__ivy_ngcc__/a/es2015/index.js', 'utf8'))
+          .toEqual('import {FooA} from "./foo";');
+      expect(readFileSync('/node_modules/test/a/es2015/index.js', 'utf8'))
+          .toEqual('import {FooA} from "./foo";');
+    });
+
+    it('should update the package.json properties', () => {
+      fileWriter.writeBundle(entryPoint, esm5bundle, [
+        {path: '/node_modules/test/a/esm5.js', contents: 'export function FooA() {} // MODIFIED'},
+      ]);
+      expect(loadPackageJson('/node_modules/test/a')).toEqual(jasmine.objectContaining({
+        module_ivy_ngcc: '../__ivy_ngcc__/a/esm5.js',
+      }));
+
+      fileWriter.writeBundle(entryPoint, esm2015bundle, [
+        {path: '/node_modules/test/a/es2015/foo.js', contents: 'export class FooA {} // MODIFIED'},
+      ]);
+      expect(loadPackageJson('/node_modules/test/a')).toEqual(jasmine.objectContaining({
+        module_ivy_ngcc: '../__ivy_ngcc__/a/esm5.js',
+        es2015_ivy_ngcc: '../__ivy_ngcc__/a/es2015/index.js',
+      }));
+    });
+
+    it('should overwrite and backup typings files', () => {
+      fileWriter.writeBundle(entryPoint, esm2015bundle, [
+        {
+          path: '/node_modules/test/a/index.d.ts',
+          contents: 'export declare class FooA {} // MODIFIED'
+        },
+      ]);
+      expect(readFileSync('/node_modules/test/a/index.d.ts', 'utf8'))
+          .toEqual('export declare class FooA {} // MODIFIED');
+      expect(readFileSync('/node_modules/test/a/index.d.ts.__ivy_ngcc_bak', 'utf8'))
+          .toEqual('export declare class FooA {}');
+      expect(existsSync('/node_modules/test/__ivy_ngcc__/a/index.d.ts')).toBe(false);
+    });
+  });
+
+  describe('writeBundle() [entry-point (with files placed outside entry-point folder)]', () => {
+    beforeEach(() => {
+      fileWriter = new NewEntryPointFileWriter();
+      entryPoint = getEntryPointInfo(_('/node_modules/test'), _('/node_modules/test/b')) !;
+      esm5bundle = makeTestBundle(entryPoint, 'module', 'esm5');
+      esm2015bundle = makeTestBundle(entryPoint, 'es2015', 'esm2015');
+    });
+
+    it('should write the modified file to a new folder', () => {
+      fileWriter.writeBundle(entryPoint, esm5bundle, [
+        {path: '/node_modules/test/lib/esm5.js', contents: 'export function FooB() {} // MODIFIED'},
+      ]);
+      expect(readFileSync('/node_modules/test/__ivy_ngcc__/lib/esm5.js', 'utf8'))
+          .toEqual('export function FooB() {} // MODIFIED');
+      expect(readFileSync('/node_modules/test/lib/esm5.js', 'utf8'))
+          .toEqual('export function FooB() {}');
+    });
+
+    it('should also copy unmodified files in the program', () => {
+      fileWriter.writeBundle(entryPoint, esm2015bundle, [
+        {
+          path: '/node_modules/test/lib/es2015/foo.js',
+          contents: 'export class FooB {} // MODIFIED'
+        },
+      ]);
+      expect(readFileSync('/node_modules/test/__ivy_ngcc__/lib/es2015/foo.js', 'utf8'))
+          .toEqual('export class FooB {} // MODIFIED');
+      expect(readFileSync('/node_modules/test/lib/es2015/foo.js', 'utf8'))
+          .toEqual('export class FooB {}');
+      expect(readFileSync('/node_modules/test/__ivy_ngcc__/lib/es2015/index.js', 'utf8'))
+          .toEqual('import {FooB} from "./foo";');
+      expect(readFileSync('/node_modules/test/lib/es2015/index.js', 'utf8'))
+          .toEqual('import {FooB} from "./foo";');
+    });
+
+    it('should update the package.json properties', () => {
+      fileWriter.writeBundle(entryPoint, esm5bundle, [
+        {path: '/node_modules/test/lib/esm5.js', contents: 'export function FooB() {} // MODIFIED'},
+      ]);
+      expect(loadPackageJson('/node_modules/test/b')).toEqual(jasmine.objectContaining({
+        module_ivy_ngcc: '../__ivy_ngcc__/lib/esm5.js',
+      }));
+
+      fileWriter.writeBundle(entryPoint, esm2015bundle, [
+        {
+          path: '/node_modules/test/lib/es2015/foo.js',
+          contents: 'export class FooB {} // MODIFIED'
+        },
+      ]);
+      expect(loadPackageJson('/node_modules/test/b')).toEqual(jasmine.objectContaining({
+        module_ivy_ngcc: '../__ivy_ngcc__/lib/esm5.js',
+        es2015_ivy_ngcc: '../__ivy_ngcc__/lib/es2015/index.js',
+      }));
+    });
+
+    it('should overwrite and backup typings files', () => {
+      fileWriter.writeBundle(entryPoint, esm2015bundle, [
+        {
+          path: '/node_modules/test/typings/index.d.ts',
+          contents: 'export declare class FooB {} // MODIFIED'
+        },
+      ]);
+      expect(readFileSync('/node_modules/test/typings/index.d.ts', 'utf8'))
+          .toEqual('export declare class FooB {} // MODIFIED');
+      expect(readFileSync('/node_modules/test/typings/index.d.ts.__ivy_ngcc_bak', 'utf8'))
+          .toEqual('export declare class FooB {}');
+      expect(existsSync('/node_modules/test/__ivy_ngcc__/typings/index.d.ts')).toBe(false);
+    });
+  });
+});
+
+function makeTestBundle(
+    entryPoint: EntryPoint, formatProperty: EntryPointJsonProperty,
+    format: EntryPointFormat): EntryPointBundle {
+  return makeEntryPointBundle(
+      entryPoint.path, entryPoint.packageJson[formatProperty] !, entryPoint.typings, false,
+      formatProperty, format, true) !;
+}