Using decorators in typescript causes a compilation error

I've been experimenting with decorators in TypeScript, but encountered an error when compiling the code:

error TS1241: Unable to resolve signature of method decorator when called as an expression.

error TS1219: Experimental support for decorators is a feature that is subject to change in a future release. Set the 'experimentalDecorators' option to remove this warning.

I've configured the decorator correctly in tsconfig.json :

{
  "compilerOptions": {
      "target"                  : "ES5",
      "experimentalDecorators"  : true,
      "emitDecoratorMetadata"   : true
  }
}

Despite trying various solutions from online resources, I haven't been able to resolve this persistent issue.

TSC version 3.4.2

One possible explanation I found is that during compilation of the TypeScript code, the decorator is being called with one less argument:

__decorate([
        f()
    ], C.prototype, "ffolow");

The following code snippet demonstrates the usage of the decorator within the "C" class:

class C {

  @f()
  ffolow() {
    console.log("FF called")
  }

}

Answer №1

The application of decorators can vary depending on how they are defined. If your decorator is classified as a 'regular' decorator (not a decorator factory), then you would typically apply it without using parentheses like in the example below:

function myDecorator(target: any, propertyName: string, descriptor: PropertyDescriptor) {
  // decorator logic here
}

class MyClass {

  @myDecorator
  myMethod() {
    console.log("Method called")
  }

}

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