Metadata

With the introduction of Classes in TypeScript and ES6, there now exist certain scenarios that require additional features to support annotating or modifying classes and class members. Decorators provide a way to add both annotations and a meta-programming syntax for class declarations and members. Decorators are a stage 2 proposal for JavaScript and are available as an experimental feature of TypeScript.

Installing

npm i @typeix/metadata --save

Creating Decorators

Defining custom decorators has not been easier, API will take care that metadataKeys are created correctly and passed to low level metadata api.

import {
    createClassDecorator,
    createParameterDecorator,
    createPropertyDecorator,
    createParameterAndPropertyDecorator,
    createMethodDecorator
} from "@typeix/metadata";

const Injectable = () => createClassDecorator(Injectable);
const Inject = (token?) => createParameterAndPropertyDecorator(Inject, {token});
const Produces = (type) => createMethodDecorator(Produces, {type});
const Render = (type) => createMethodDecorator(Produces, {type});
const PathParam = (value) => createParameterDecorator(Produces, {value});

@Injectable()
class AService {
}

@Injectable()
class BService {
}

@Injectable()
class RootController {
    @Inject() aService: AService;
    @Inject() bService: BService;

    @Produces("application/json")
    actionIndex(@Inject() first: AService, @Inject() second: BService) {
    }
}

@Injectable()
class HomeController extends RootController {

    @Render("home")
    actionHome(
        @Inject() first: AService,
        @Inject(BService) second: BService,
        @PathParam("name") name: string
    ) {
    }
}

const metadata: Array<IMetadata> = getAllMetadataForTarget(HomeController);

Interface IMetadata

• args - are custom arguments passed by decorator
• metadataKey - is unique decorator key auto generated by metadata api
• type - class, method, property, parameter
• decoratorType - (above type) + mixed is createParameterAndPropertyDecorator
• decorator - actual reference to decorator Function
• propertyKey - user defined method name or constructor
• paramIndex - it's defined if decorator is parameter type
• designType - value from design:type typescript metadata
• designParam - values from design:paramtypes typescript metadata
• designReturn - values from design:returntype typescript metadata

  export interface IMetadata {
      args: any;
      metadataKey: string;
      type?: string;
      decoratorType?: string;
      decorator?: Function;
      propertyKey?: string | symbol;
      paramIndex?: number;
      designType?: any;
      designParam?: any;
      designReturn?: any;
  }
  

  All metadata for target can be requested via getAllMetadataForTarget function, which returns list of metadata.
  eg.:

  [
      {
          args: {
              token: BService
          },
          decoratorType: "mixed",
          decorator: Inject,
          type: "parameter",
          metadataKey: `@typeix:parameter:Inject:1:${getDecoratorUUID(Inject)}`,
          paramIndex: 1,
          propertyKey: "actionHome",
          designParam: [
              AService,
              BService,
              String
          ]
      }
      ...
  ]