typescriptDecorators.ts

// A decorator is a function that can be used to modify/change different properties or methods in a class
// They are used inside/on classes only
// Understanding the orde that they are run is important in using decorators

// Decorators can be used on properties, methods or accessors(getters and setters);
// First argument is the prototype
// Second argument is the key ( the method, accessor or property)
// Third argument is the property descriptor
// We want to use a decorator factory as such that takes in externat arguments
const Logging = (message: string) => {
  return (target: any, key: string, desc: PropertyDescriptor): void => {
    const method = desc.value;
    desc.value = () => {
      try {
        method();
      } catch (e) {
        console.error(message);
      }
    };
  };
};

const params = (target: any, key: string, index: number) => {
  console.log("key: ", key, " index: ", index);
};

const classDef = (constructor: typeof Boat) => {
  console.log("constructor: ", constructor);
};

@classDef
class Boat {
  // Note you cannot modify properties with decorators as they are stored on the constructor object
  // what is made available to us is the prototype object that contains methods
  public color = "red";

  get formattedColor(): string {
    return `The boat is ${this.color}`;
  }

  @Logging("Cannot drive this boat")
  public drive(@params speed: string, @params driver: string): void {
    throw new Error("Cannot drive this car yet");
  }
}