decorator-runtime-order.ts

function deco(
  target: any,
  propertyKey: string,
  descriptor: PropertyDescriptor
) {
  console.log(`method "${propertyKey}" decorator: begin`);
  if (descriptor === undefined) {
    descriptor = Object.getOwnPropertyDescriptor(target, propertyKey);
  }
  const originalMethod = descriptor.value;
  let i = 0;

  descriptor.value = function (...args: any[]) {
    const id = `${propertyKey}_${i++}`;
    console.log(`${id}: begin`);
    const result = originalMethod.apply(this, args);
    console.log(`${id}: end`);
    return result;
  };
  console.log(`method "${propertyKey}" decorator: end`);
  return descriptor;
}

class Person {
  constructor() {
    console.log(`Class Constructor: called`);
  }

  @deco
  sayHi() {
    console.log('\t Hi');
  }

  @deco
  sayBye() {
    console.log('\t Bye');
  }
}

function main() {
  console.log(`Main: Start`);
  const p1 = new Person();
  p1.sayBye();
  p1.sayBye();
  const p2 = new Person();
  p2.sayBye();
  p2.sayBye();
}

main();