Method decorators in class expressions are silently ignored.

TypeScript Version: 3.2

Search Terms:

• decorators
• class expressions

Code

const decorator = () => null;

// This calls __decorate with decorator.
class Statement {
  @decorator()
  method() {

  }
}

// This doesn't! It also doesn't produce a compiler error of any kind.
(class Expression {
  @decorator()
  method() {

  }
})

Expected behavior:

__decorate should be called, or a compiler error should be produced.

Actual behavior:

The decorator is silently ignored, omitting it from the decoration compiled output.

Playground Link:

https://www.typescriptlang.org/play/index.html#src=const decorator %3D () %3D> null%3B class Statement { %40decorator() method() { } } (class Expression { %40decorator() method() { } })

Related Issues:

• Using decorators on arguments in class expressions produces a compiler error: https://github.com/Microsoft/TypeScript/issues/7342

• This one is about decorators on class expressions, not methods within a class expression: https://github.com/Microsoft/TypeScript/issues/15975 - but produces some kind of error at least.

[brandonbloom]

For what it’s worth as input to your issue classification process: The project in which this issue was discovered has some decorators that are performing access control for an HTTP API. Switching from Babel to TypeScript with allowJS meant that a bunch of security was silently turned off!

On Sun, Dec 9, 2018 at 10:56 PM Daniel Rosenwasser [e-mail] wrote:

So what’s the deal, would we consider this a bug or a design limitation?

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[DanielRosenwasser]

So what’s the deal, would we consider this a bug or a design limitation?