What is Angular Package Format?

The Angular Package Format (APF) is a set of standards and recommendations for the structure and content of Angular libraries published to npm. Its primary goal is to ensure that Angular libraries are compatible with the Angular ecosystem, optimized for various compilation modes (JIT, AOT), and easy to consume for developers.

What is APF?

APF defines a consistent way for Angular libraries to be structured and built, allowing tools like the Angular CLI and bundlers (e.g., webpack, Rollup) to efficiently process and optimize them. It addresses the complexities of packaging libraries that need to support multiple environments, module formats, and Angular's advanced compilation features like AOT.

Key Goals of APF

• Standardization: Provide a uniform structure for all Angular libraries, making them predictable and easier to use.
• Optimization: Ensure libraries are pre-optimized for AOT compilation and tree-shaking to produce smaller, faster applications.
• Compatibility: Support various module formats (ESM, CommonJS, UMD) and different JavaScript targets (ES2015, ES2020, etc.) to cater to diverse build environments.
• Type Safety: Include TypeScript declaration files (.d.ts) to provide type safety and improved developer experience.
• Future-Proofing: Design the format to be adaptable to future changes in Angular and the JavaScript ecosystem.

Structure and Contents

An Angular library conforming to APF will typically contain multiple output formats and metadata files within its published npm package. This allows bundlers to pick the most optimal version for the target application.

• fesm2022/ (Flattened ES Modules for ES2022): Contains ES modules that have been 'flattened' (all modules merged into one file). This is optimized for modern bundlers and tree-shaking.
• esm2022/ (ES Modules for ES2022): Individual ES modules, also for modern bundlers, but not flattened.
• fesm2015/ (Flattened ES Modules for ES2015): Similar to fesm2022 but targeting ES2015 for broader compatibility.
• bundles/ (UMD Bundles): Contains Universal Module Definition (UMD) bundles, which can be used in various environments, including direct browser script tags.
• typings/ or dist/ (TypeScript Declaration Files): .d.ts files providing type definitions for the library's public API.
• package.json: The root package.json of the library, which includes metadata and points to the different entry points (e.g., main, module, es2022, typings) for bundlers to use.

Benefits of APF

• Improved Developer Experience: Consumers of Angular libraries don't need to worry about the underlying build process; libraries just work.
• Optimized Applications: Libraries are pre-optimized for tree-shaking and AOT, resulting in smaller bundle sizes and faster application startup times.
• Consistency Across Ecosystem: Fosters a unified approach to library publishing, making the Angular ecosystem more robust and predictable.
• Reduced Build Time: Applications consuming APF-compliant libraries spend less time transforming the library code during their own build process.

How is it created?

The primary tool for creating APF-compliant Angular libraries is ng-packagr. This build tool automates the process of transpiling, bundling, and generating all the necessary output formats and metadata required by the Angular Package Format from a standard Angular project.