Outline

export function TypedParam(name: string): ParameterDecorator;

Type safe path parameter decorator.

@TypedParam() is a decorator parsing path parameter.

It's almost same with original @Param() function of NestJS, however, @TypedParam() is more type safe.

As @TypedParam() can anlayze source code in the compilation level, it can specify parameter type by itself. Also, while NestJS cannot distinguish nullable type and consider every parameter value as a string type, @TypedParam() can do it. Furthermore, @TypedParam() can validate special types like "uuid" or "date".

Let's read below example code, and see how @TypedParam() works.

How to use

import { TypedParam } from "@nestia/core";
import { Controller, Get } from "@nestjs/common";
import { tags } from "typia";
 
@Controller("parameters")
export class ParametersController {
  @Get("uint32/:value")
  public async uint32(
    @TypedParam("value") value: (number & tags.Type<"uint32">) | null,
  ): Promise<(number & tags.Type<"uint32">) | null> {
    return value;
  }
 
  @Get("string/:value")
  public async string(
    @TypedParam("value") value: string
  ): Promise<string> {
    return value;
  }
 
  @Get("uuid/:value")
  public async uuid(
    @TypedParam("value") value: string & tags.Format<"uuid">,
  ): Promise<string> {
    return value;
  }
}

Just call @TypedParam() function on the path paremeter, that's all.

If you want to special parameter type like "uint32" or "uuid", utilize type tags of typia (opens in a new tab).

When wrong typed value comes, 400 bad request error would be thrown.

Restriction

@TypedParam() allows only atomic type.

• boolean
• number
• string
• bigint

Also, @TypedParam() allows nullable like number | null, but undefindable type is not.

• number | null is allowed
• string | undefined is prohibited

If you violate above condition, and try to declare object or union type, compilation error would be occured:

Error on nestia.core.TypedParam(): only atomic type is allowed