Angular Package Format: Standardizing Angular Libraries

Anton Ioffe - December 9th 2023 - 9 minutes read

Embarking on a journey through the heart of Angular's architectural symphony, this article peels back the layers of the Angular Package Format (APF), a blueprint critical to the art and science of crafting Angular libraries. As we dissect the tenets that hold up this foundational technology, our path will wind through the evolution of APF's modular design, the delicately balanced scales of performance, and the impact these have on the trenches of development experience. We'll delve into the nuances that make up the developer's dance with standardization, stirring a reflection on its constraints and freedoms. Prepare to have your notions both challenged and fortified as you navigate the comprehensive trails of APF, unlocking a realm of insights poised to elevate your prowess in Angular library development.

Angular Package Format: The Pillars of Angular Libraries

The Angular Package Format (APF) can be seen as the blueprint for distributing reusable Angular libraries. It meticulously outlines the guidelines for compiling, bundling, and packaging these libraries so that they can be effortlessly consumed within an Angular ecosystem. At its core, APF lays out the standards for file format, metadata structure, and artifacts that a library must adhere to for seamless import and usage by developers across various Angular projects.

APF dictates the structure of an Angular library in a way that ensures consistent compilation outputs which include, among other things, metadata files and JavaScript bundles. These outputs are designed to be AOT (Ahead-of-Time) compilable, granting the consuming applications the benefits of performance optimizations that come with AOT. A pivotal structure within the APF is the directory layout it recommends, where each distributable part of the library is neatly encapsulated within specific folders, reinforcing a clean separation of concerns.

The format specification includes provisions for FESM (Flat ECMAScript Module), which are ECMAScript modules that bundle all JavaScript into a single file per module, and UMD (Universal Module Definition) bundles, which ensure compatibility with different module loaders such as AMD, CommonJS, and the global variable style. The APF recommends the FESM2015 format for packaging as it's especially aligned with the modern JavaScript syntax and promotes tree-shaking – a process to eliminate dead code and reduce the final bundle size.

To cater to the tooling ecosystem around Angular, APF includes the distribution of type definitions files, which enhances the development experience by providing auto-completion, navigation, and refactoring capabilities suited for TypeScript developers. Libraries packaged in line with APF contain .d.ts files adjacent to their corresponding .js files, which allows for a type-checked interface to the library's API.

The Angular Package Format’s approach to handling entry points further streamlines library development. An entry point is a facet of a library that will be referenced by applications or other libraries and serves as the end point of a dependency graph. The package.json file within each entry point specifies the module resolutions with mappings to the corresponding FESM2015 and UMD bundles. This structured approach to entry points enables finer control over what parts of the library are exposed for public API consumption and facilitates better tree-shaking and bundling strategies during the build process of consuming applications.

APF Evolution and Modularity

With the release of Angular v13, the Angular team introduced a series of updates to the Angular Package Format (APF) that effectively refined its modularity. A modular library structure is pivotal for clean code separation and effective lazy loading, resulting in performance gains. By embracing more modern JavaScript output formats such as ES2020, Angular libraries can now leverage improved tree-shaking, which reduces bundle sizes by excluding unused code. This move away from the legacy View Engine-specific metadata and toward Ivy's leaner compilation artifacts simplifies the deployment mechanism, steering developers toward creating more modular, maintainable, and reusable code. The omission of ngcc indicates a paradigm shift in ensuring that libraries are seamlessly integrated with the Ivy compiler, enhancing the consistency of build outputs and subsequently boosting modularity within the Angular ecosystem.

The transition to ES2020 modules and the removal of outdated View Engine formats impact the complexity and modularity of Angular projects. For instance, older versions required in-depth knowledge of the Angular compiler and its compatibility requirements, whereas the simplified approach in v13 abstracts the complexities, allowing developers to focus more on the architecture and less on configuration. Modularity is further emphasized by the inclusion of Node Package Exports in the package.json, which aids in encapsulating library internals. This encapsulation fortifies API boundaries, ensuring that internal changes do not affect consumers of the library, thereby fostering a modular approach to library consumption and development.

From a performance perspective, these advancements imply that Angular applications can now benefit from faster compilation times and smaller bundles. Such improvements are particularly noticeable in large-scale applications where numerous modules and libraries interplay. Modular Angular libraries can be more effectively treeshaken and lazy-loaded, ensuring that applications load only necessary code, which can lead to improved startup times and enhanced user experience.

To illustrate the modularity enabled by the recent changes, consider the development of a feature-rich data table library. Prior to Angular v13, such a library might include a monolithic bundle containing a vast array of components, directives, pipes, and services, irrespective of their use in the consumer application. However, with the modular principles promoted by the updated APF, such a library can efficiently organize its offerings into discrete entry points. As a result, an application can import only the specific modules it requires, such as sorting functionality or pagination, thus adhering to the principles of modularity and reusability.

The consequences of these APF changes manifest in real-world scenarios where the complexity of managing an Angular library is significantly diminished. Developers now have a streamlined process for updating their libraries to align with the latest APF standards, often resulting in a "cleaner" and more approachable codebase. It's a transformation that not only benefits the current state of library development but strategically positions Angular to take advantage of future web platform enhancements, ensuring that Angular modules remain at the forefront of web development practices.

Performance Implications in APF's Design

Significant advancements in library performance are achieved through strategic employment of the Angular Package Format's design. Transitioning to ES2020 modules pays dividends in performance, notably by enhancing tree-shaking efficiency, a mechanism that eliminates dead code, leading to lighter and faster applications.

A closer look at the build process reveals the tangible benefits of this approach. Previously, builds required a ngcc post-install step, creating a bottleneck that is now eliminated. Consider the previous and updated build scripts:

// Previous build script
"scripts": {
    "postinstall": "ngcc",
    "build": "ng build --prod",
    // Additional build steps

// Updated build script after APF enhancements
"scripts": {
    // Note ngcc step is no longer required
    "build": "ng build --prod",
    // Additional build steps

By omitting outdated formats and metadata, APF v13 results in leaner packages that optimize both loading times and memory usage. The lighter packages afford faster resolution of modules across development and runtime environments.

Adhering to modular principles by dividing libraries into independent components improves tree-shaking effectiveness. Each discrete module encapsulates functionality providing high cohesion and low coupling, as shown in this modularity-driven design:

// Component within a feature module, making use of ES2020 exports
export class LoginComponent {
    // Login component functionality

// Feature module only exporting necessary components and services
export class AuthModule {
    // Components like LoginComponent are exported for external use
    // Only the required components and services are loaded, thanks to tree-shaking

// Application module benefiting from selective imports, enhancing load performance
import { AuthModule } from 'my-auth-library';

export class AppModule {
    // AppModule is leaner as it includes only what is necessary from AuthModule

In practice, ES2020 modules allow for more effective code elimination by bundlers. As a result, every extraneous byte that can be avoided directly benefits large-scale applications where performance is paramount.

Finally, optimizing library construction requires meticulous focus on performance. Keeping libraries up-to-date with the latest APF advancements ensures that developers can leverage these speed and memory-usage optimization opportunities.

APF's Role in Enhancing Developer Experience

The Angular Package Format is deeply intertwined with the developer experience, primarily by simplifying the packaging and consumption of Angular libraries. Its influence extends to enhanced readability—developed libraries can be scrutinized more easily, especially when tracing through dependencies defined in package.json. However, a common mistake is for developers to inadvertently expose internal APIs, which should remain private to the library. A proactive measure is to define entry points using the exports field in package.json. By doing so, developers create a clear contract for consumers, guarding against reliance on internal mechanics that could change unexpectedly.

Reusability is another facet where APF shines. It prescribes a structure that naturally promotes the creation of modules that can be imported across different projects. An oft-seen pitfall is when developers needlessly duplicate code across multiple modules, leading to bloat and potential synchronization issues. By following APF guidelines to architect libraries with discrete, reusable modules, this redundant practice can be avoided. For example, creating a utility module within the library, hosting commonly used functions, can significantly dry up the codebase.

Maintenance is a critical aspect of the development lifecycle where APF provides significant benefits. As Angular libraries evolve, the clear-cut standards and practices prescribed by APF make upgrading and refactoring efforts more straightforward and predictable. However, developers must remain vigilant about backward compatibility. For instance, introducing breaking changes without adhering to semantic versioning is a frequent oversight. Addressing this involves meticulous planning of versions and clear communication through changelogs, which APF encourages through its strict versioning discipline.

// Incorrect: Publicly exposing all internals
"exports": {
    "./*": "./dist/my-lib/*"
// Correct: Exposing only public API
"exports": {
    ".": {
        "import": "./dist/my-lib/public-api.js",
        "require": "./dist/my-lib/public-api.umd.js"

The above code showcases a correction where only the public API is exported, rather than all internal files. This not only prevents misuse but enhances security and simplifies the developer's task when using the library.

To invite further contemplation, consider the broader implications of a well-implemented APF. How does it not only facilitate the current project's scalability but also prepare the code for unforeseen future requirements? What strategies can be implemented to ensure that APF's full potential in maintaining a robust and adaptable codebase is realized? Reflecting on these questions can lead to a richer understanding of APF's role in your development workflow.

Adhering to and Stretching Beyond Standardization

Adhering strictly to the Angular Package Format can sometimes feel like placing creative problem-solving in a straitjacket. On one side, the APF offers a well-constructed framework that ensures Angular libraries are efficient, compatible, and maintainable across the ecosystem. Utilizing standardized practices like ES2020 module syntax and omitting View Engine-specific metadata promotes consistency and leverages modern JavaScript capabilities. It simplifies the developer's task, enabling them to focus on delivering functionality rather than configuring their package structures.

However, innovation often requires a degree of experimentation that bends or even temporarily disregards the norms. Striking a balance between the two—conformance and exploration—is key. While the temptation to create something entirely unique can be strong, stepping too far outside the boundaries of APF standards might lead to compatibility issues, potentially hindering the adoption rate of the library and increasing the maintenance burden.

The real challenge lies in finding creative solutions within the constraints of the APF. How can you employ ingenuity to extend Angular's capabilities while still ensuring your solution adheres to the expectations for modularity and efficiency? It requires a deep understanding of both the framework's architecture and the evolving needs of developers. By working within the guidelines, you stretch your expertise and raise the standard of your work, offering a library that not only integrates flawlessly but also stands out for its innovation.

Consider using Node Package Exports wisely to expose a stable and thoughtfully curated API from your library without overexposing internal structures that could change. The discipline of maintaining well-defined API boundaries not only streamlines the consumer experience but also encourages a modular and maintainable codebase. Furthermore, anticipate the impact of your design choices on the library's performance and future scalability. Are there ways to optimize for tree-shaking without compromising on the complex features you want to provide?

In crafting exceptional Angular libraries, one must question whether every innovation yields a net benefit. Is there a way to push the envelope to provide unique, high-quality features while respecting the standards that ensure cohesion in the Angular ecosystem? Reflecting on this balance will guide you in creating powerful, standard-conforming libraries that are both imaginative and technically excellent.


The article explores the Angular Package Format (APF) and its role in standardizing Angular libraries. It delves into the structure and specifications of APF, highlighting its impact on modularity, performance, and developer experience. Key takeaways include the importance of adhering to APF guidelines for creating efficient and reusable libraries, the performance benefits of utilizing ES2020 modules and tree-shaking, and the need to strike a balance between conforming to standards and exploring innovative solutions. To further explore the concept of modularity and performance optimization in Angular libraries, readers are challenged to analyze their own libraries and identify opportunities for enhancing tree-shaking and reducing bundle size without compromising complex features.

Don't Get Left Behind:
The Top 5 Career-Ending Mistakes Software Developers Make
FREE Cheat Sheet for Software Developers