Extract out the typescript bits into its own preset

[jdalton]

I'd like to point folks to a Babel alternative for their TypeScript projects. I noticed you cover the feature gaps-and-fills here. Do you see a benefit to breaking out the preset into a TypeScript preset instead of scoping it to just Angular2?

[shuhei]

I haven't thought about it but the preset does nothing more than emulating a part of TypeScript's emitDecoratorMetadata and experimentalDecorators, and does nothing Angular-specific. But it currently supports only metadata that are used by Angular 2. I haven't looked at it carefully but there seems to be other metadata that are not supported yet. To make it a TypeScript preset, we still need some effort.

I still don't have any idea about use cases without Angular 2. What kind of projects are in your mind?

[shuhei]

babel-plugin-angular2-annotations, the core of the preset, does the following:

• parameter decorators -> metadata
• type annotations -> metadata
• fix a bug on class properties without initializers

They could be extracted as separated plugins if necessary.