Decorators (Experimental) – Class & Method

Enabling Decorators

Add to tsconfig.json:

"experimentalDecorators": true,
"emitDecoratorMetadata": true

Class Decorator Example

function sealed(constructor: Function) {
  Object.seal(constructor);
  Object.seal(constructor.prototype);
}

@sealed
class Service {
  // …
}

Method Decorator – Logging

function log(target: any, propertyKey: string, descriptor: PropertyDescriptor) {
  const original = descriptor.value;
  descriptor.value = function (...args: any[]) {
    console.log(`Calling ${propertyKey} with`, args);
    return original.apply(this, args);
  };
}

class MathOps {
  @log
  add(a: number, b: number) {
    return a + b;
  }
}