ts-r
  • Error
  • Reported by the lexer and parser

TS1497

Expression must be enclosed in parentheses to be used as a decorator.

A decorator expression is more than a name, property access or call. Wrap the expression in parentheses.

What it means

Decorators only accept a simple form: @name, @a.b.c or a call like @factory(). Anything else, such as an element access or a call on a computed value, must be put in parentheses.

Example

index.ts
declare const registry:
  | { service(target: unknown, context: ClassDecoratorContext): void }
  | undefined;

@registry?.service
export class Service {}
ts-r-check -p tsconfig.json --pretty false ts-r output
index.ts(5,2): error TS1497: Expression must be enclosed in parentheses to be used as a decorator.

Recorded by node scripts/verify-examples.mjs with ts-r built from commit 6deaf01. The example uses the default tsconfig: strict, target: es2022, module: esnext, moduleResolution: bundler.

How to fix

  • Wrap it: @(registry?.service), or narrow first and use a plain name.