babel-plugin-transform-typescript-metadata weekly downloads statistics

babel-plugin-transform-typescript-metadata

Babel plugin to emit decorator metadata like typescript compiler

Motivation

TypeScript _Decorators_ allows advanced reflection patterns when combined with Reflect.metadata output.

Current @babel/preset-typescript implementation however just strips all types and _does not_ emit the relative Metadata in the output code.

Since this kind of information is used extensively in libraries like Nest and TypeORM to implement advanced features like Dependency Injection, I've thought it would be awesome to be able to provide the same functionality that TypeScript compiler experimentalDecorators and emitDecoratorMetadata flags provide.

This means that code like:

will be interpreted like:

Parameter decorators

Since decorators in typescript supports also _Parameters_, this plugin also provides support for them, enabling the following syntax:

This will be roughly translated to:

Installation

With npm:

or with Yarn:

Usage

With .babelrc:

Note: should be placed before @babel/plugin-proposal-decorators.

Usage with InversifyJS

If you are using normal dependency injection letting Inversify create your instances, you should be fine with all kind of decorators.

Instead, if you are using property injection, when the container does not create the instances, you would likely encounter errors since babel decorators are not exactly the same as TypeScript.

You can fix it by _enhancing property decorators_ with the following function:

Current Pitfalls

• If you are using webpack and it complains about missing exports due to types not being removed, you can switch from import { MyType } from ... to import type { MyType } from .... See #46 for details and examples. • We cannot know if type annotations are just types (i.e. IMyInterface) or concrete values (like classes, etc.). In order to resolve this, we emit the following: typeof Type === 'undefined' ? Object : Type. The code has the advantage of not throwing. If you know a better way to do this, let me know!

Description from the npm listing.