dtty

Dependency Injection + Itty Router = dtty.

Web framework for Cloudflare workers inspired by NestJS.

Initialization

To use Dtty, simply create a new instance and let it handle all incoming requests.

// index.ts
const app = new Dtty();

export default {
  async fetch(
    request: Request,
    env?: Record<string, any>,
    ctx?: ExecutionContext,
  ): Promise<Response> {
    return app.handle(request, env, ctx);
  },
};

Routing

Controllers are registered through the Dtty.registerControllers method. This handles the mapping of routes and application of controller level and method level middleware.

@Controller("/route")
class RouteController {
  @Get("/")
  handleGet() {}

  @Post("/")
  handlePost() {}

  @Put("/")
  handlePut() {}

  @Delete("/")
  handleDelete() {}
}

/* ----- */
app.registerControllers(
  // Array of controller classes
  RouteController,
);

Route params

Route parameters can be injected into controller methods with the @Param() decorator which takes an optional string to inject an individual parameter as opposed to all the parameters.

Optionally, the @Param() decorator takes a second parameter that to parse and validate the parameter. For example, if an endpoint expects an id parameter of type number (e.g /request/1234), the included IntegerTransformer will automatically validate that the parameter is an integer and will transform the string into an integer before supplying it to the controller handler.

Included Transformers

• IntegerTransformer
• UuidTransformer

@Get('/route/:id')
getRouteById(@Param("id") id: string) {}

@Get('/route/:id')
getRouteByNumberId(@Param("id", IntegerTransformer) id: number) {}

Query Params

Much like route parameters, query parameters can be injected into the controller with the @Query() decorator. The decorator takes a configuration object to inject either an individual parameter or all the parameters with optional transformation and validation.

When working with esbuild, some of the metadata that typescript emits and class-transformer relies upon is missing. Therefore, all class properties should be decorated with the @Type decorator to manually specify the type of the field.

  @Get('/named')
  handleNamedParam(@Query({paramName: "test"}) value: string) {
    // maps the parameter named `test` out without transformation
  }

  @Get('/unnamed')
  handleUnnamed(@Query() values: Record<string, unknown>) {
    // maps all the query parameters out without transformation or validation
  }

  @Get('/named/transformed')
  handleNamedAndTransformed(@Query({paramName: "test", transformer: IntegerTransformer}) value: number) {
    // maps the parameter named `test` out and transforms into an integer
  }

  @Get('/unnamed/validated')
  handleUnnamedAndValidated(@Query({paramsType: QueryDto}) values: QueryDto) {
    // maps all the query parameters out and transforms and validates against a class definition
  }

Body

The request body can be both validated and injected into controller methods via the @Body() decorator. This decorator optionally takes a class constructor to perform transformation and validation via class-transformer and class-validator respectively.

@Put('/route/:id')
updateRouteById(@Param('id') id: string, @Body(UpdateRouteDto) body: UpdateRouteDto) {}

Exception Handling

Exceptions thrown by an endpoint are caught at three levels:

• Method
• Controller
• Global

Dtty provides an interface called ExceptionHandler to define how classes can be used to catch and handle exceptions. The HandleException decorator optionally takes a parameter to filter exceptions by type to enable finer grained control over exception handling logic. For a given exception:

1. Evaluate any method level exception handlers for the specific exception type
2. Evaluate any un-filtered method level exception handlers
3. Evaluate any controller level exception handlers for the specific exception type
4. Evaluate any un-filtered controller level exception handlers
5. Evaluate any global level exception handlers for the specific exception type
6. Evaluate any un-filtered global level exception handlers

If no exception handlers are found, the application will return with code 500.

@Controller()
@ApplyHandlers(ControllerExceptionHandler)
export class IndexController {
  @Get("")
  @ApplyHandlers(MethodExceptionHandler, GenericHandler)
  getIndex() {}
}

Roadmap

• Global middleware
• Controller middleware
• Route middleware
• Global body transformer
• Global body validator
• Route param transformer / validator
• Global exception handler
• Controller exception handler
• Route exception handler
• URL query param mapper
• URL query param transformer / validator
• Optimizations for tree shaking
• Custom DI library
• UUID transformer
• Async constructors