createParamDecorator return type safety | NestJS | Page 1

stone monolith Jan 14, 2024, 3:09 PM

#

lets say i have created this decorator which is in the docs

  (data: unknown, ctx: ExecutionContext) => {
    const request = ctx.switchToHttp().getRequest();
    return request.user;
  },
);```

and i want to call it for example in this controller

@Controller('posts')
export class PostController {
@UseGuards(JwtGuard)
@Get('
getAllPosts(
//decorator call
@GetUser() user // this is any) {
return {data};
}
}

is it possible for the user type to be inferred from the decorator?
I can set it in the controller to any type i want which is not type safe

high dew Jan 14, 2024, 3:46 PM

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nop

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there is no such thing as type inference for parameters decorators in typescript

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but I like to follow this convention:

foo(@GetUser() user: GetUser) {}

ie., create a type with the same name of the decorator factory

#

you can find how here: https://dev.to/micalevisk/nestjs-tip-type-safety-on-parameter-decorators-24mn

DEV Community

NestJS tip: type safety on parameter decorators

for NestJS v8, v9 and v10 In NestJS we can create specialized kind of parameters decorators using...

stone monolith Jan 14, 2024, 6:55 PM

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I meant like the returned object is known and should be applied to the variable

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i guess it's a typescript limitation

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thank you

high dew Jan 14, 2024, 7:58 PM

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yes, it is

cinder needleBOT Jan 14, 2024, 7:58 PM

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This post has been marked as resolved. :white_check_mark:
Please read through the conversation and resolution if you are having the same issue, and then re-open the post if you are still having trouble, providing as much extra information as possible.

sturdy edge Apr 18, 2026, 6:54 PM

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@high dew 🇧🇷 does GetUser needs to a class ?

i dont this typescript type or interface can work in parameters

high dew Apr 18, 2026, 6:55 PM

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Sorry, I didnt understand your question

sturdy edge Apr 18, 2026, 6:59 PM

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  @Get('getProfile')
  @HttpCode(HttpStatus.OK)
  @UseGuards(AuthGuard, RoleGuard)
  @RoleDecorator([RoleEnum.USER])
  async getProfile(@CurrentUserDecorator() user: UserLeanType): Promise<AppResponseDto> {
    return await this.userService.getProfile(user);
  }

like here UserLeanType is a class, this works

but if i use type or interface it throws error

high dew Apr 18, 2026, 7:00 PM

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What is the error? I don’t think that the CurrentUserDecorator requires that but it depends on what the decorator does

sturdy edge Apr 18, 2026, 7:01 PM

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export class UserLeanType {
  _id: string;
  firstName: string;
  lastName: string;
  email: string;
  dob: string;
  phoneNumber: string;
  verified: boolean;
  active: boolean;
  role: RoleEnum;
}

i am usign "UserLeanType" to have types for my "user"

#

but if i use interface or typescript type then i get error

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SyntaxError: The requested module '../../type/userLean.type.js' does not provide an export named 'UserLeanType'
    at ModuleJob._instantiate (node:internal/modules/esm/module_job:228:21)
    at async ModuleJob.run (node:internal/modules/esm/module_job:335:5)
    at async onImport.tracePromise.__proto__ (node:internal/modules/esm/loader:647:26)
    at async asyncRunEntryPointWithESMLoader (node:internal/modules/run_main:117:5)

this is the error i get when "UserLeanType" is typescript type or interface

but wneh it a class as mentions then it works, no error

high dew Apr 18, 2026, 7:07 PM

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Are you using tsc as the builder for nestjs cli? It is the default

sturdy edge Apr 18, 2026, 7:07 PM

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{
  "$schema": "https://json.schemastore.org/nest-cli",
  "collection": "@nestjs/schematics",
  "sourceRoot": "src",
  "compilerOptions": {
    "deleteOutDir": true,
    "builder": {
      "type": "swc",
      "options": {
        "swcrcPath": "./.swcrc"
      }
    },
    "typeCheck": true
  }
}

i am using swc

high dew Apr 18, 2026, 7:07 PM

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Try it out with tsc please

sturdy edge Apr 18, 2026, 7:08 PM

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ok

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will update here

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@high dew is this an issue or expected result

high dew Apr 18, 2026, 7:20 PM

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sturdy edge <@132222189209518080> is this an issue or expected result

That code its fine
Also, If it works with tsc it should work with swc builder. But it could be just a minor config issue on your side

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I didnt use the swc too much tho

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tsc is fast and reliable enough so far for my projects

sturdy edge Apr 18, 2026, 7:21 PM

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apparantly i have set up the code base with ESM focused.

tsconfig.json
{
  "compilerOptions": {
    "module": "NodeNext",
    "moduleResolution": "NodeNext",
    "lib": ["ESNext"],
    "target": "ESNext",
    "outDir": "./dist",
    "sourceMap": true,
    "noEmit": true,
    "removeComments": true,
    "checkJs": true,
    "strict": true,
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true,
    "esModuleInterop": true,

    "declaration": true,
    "allowSyntheticDefaultImports": true,
    "incremental": true,
    "skipLibCheck": true,
    "strictNullChecks": true,
    "forceConsistentCasingInFileNames": true,
    "noImplicitAny": true,
    "strictBindCallApply": true,
    "noFallthroughCasesInSwitch": true,
    "strictPropertyInitialization": false
  },
  "include": ["src/**/*", "test/**/*"],
  "exclude": ["node_modules", "dist"]
}

swcrc
{
  "$schema": "https://swc.rs/schema.json",
  "sourceMaps": true,
  "minify": false,
  "module": {
    "type": "es6",
    "strict": false,
    "strictMode": true,
    "lazy": false,
    "noInterop": false
  },
  "jsc": {
    "externalHelpers": true,
    "target": "esnext",
    "loose": false,
    "keepClassNames": true,
    "preserveAllComments": false,
    "parser": {
      "syntax": "typescript",
      "tsx": false,
      "decorators": true,
      "dynamicImport": true
    },
    "transform": {
      "legacyDecorator": true,
      "decoratorMetadata": true
    }
  }
}

high dew Apr 18, 2026, 7:22 PM

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Yes. This is another thing to have in count. It should not be a problem

#createParamDecorator return type safety