How do you create a custom parameter decorator in NestJS?

Q: How do you create a custom parameter decorator in NestJS?

// current-user.decorator.ts export const CurrentUser = createParamDecorator( (data: keyof User | undefined, ctx: ExecutionContext) => { const request = ctx.switchToHttp().getRequest(); const user = request.user; // If data is passed (e.g. @CurrentUser('email')), return that field return data ? user?.[data] : user; }, ); // Usage in controller @Get('profile') @UseGuards(JwtAuthGuard) getProfile(@CurrentUser() user: User) { return user; } @Get('email') @UseGuards(JwtAuthGuard) getEmail(@CurrentUser('email') email: string) { return email; } createParamDecorator takes a factory function that receives data and ctx. data is the argument passed to the decorator at the call site. ctx.switchToHttp().getRequest() gives the underlying HTTP request. Custom param decorators can be combined with pipes for validation.

Difficulty: 5/10

custom decorators, metadata reflection, request handling

Use createParamDecorator which receives a factory function with (data, ctx) arguments. The data argument is whatever is passed into the decorator at usage time, and ctx is the ExecutionContext providing access to the request, response, and other context.

Custom @CurrentUser() decorator

Key points:

1
createParamDecorator takes a factory function that receives data and ctx.
2
data is the argument passed to the decorator at the call site.
3
ctx.switchToHttp().getRequest() gives the underlying HTTP request.
4
Custom param decorators can be combined with pipes for validation.

Scenario Questions

0-2 years experience

Follow-up Questions