abstract.js

export function abstract() {
  return (cls, prop, descriptor) => {
    if (prop === undefined) {
      return class Abstract extends cls {
        constructor(...args) {
          super(...args);
          
          if (this.constructor === Abstract) {
            throw new Error('Class is abstract, and should not be instansiated.');
          }
        }
      };
    }
    
    function abstract() {
      throw new Error(`Method "${prop}" is abstract, and should have been overridden in a subclass.`);
    }
    
    if (descriptor.value) {
      // this is a method
      descriptor.value = abstract;
    } else {
      // property (getter and/or setter)
      if (descriptor.get) {
        descriptor.get = abstract;
      }
      
      if (descriptor.set) {
        descriptor.set = abstract;
      }
    }
  };
}

usage.js

@abstract()
class Abstract {
  @abstract()
  get foo() {
    
  }
  
  @abstract()
  bar() { }
}

class Actual extends Abstract {
  get foo() {
    return 'foo';
  }
  
  bar() {
    return 'bar';
  }
}