TypeScript 5.0 decorators.

decorators.ts

class DecoratorDemo {
  @log
  public do() {
    console.log('BLIP');
  }
}

const d = new DecoratorDemo();
d.do();

function log(target: any, context: any) {
  const methodName = context.name || 'Unknown';

  function replacementMethod(this: any, ...args: any[]) {
    console.log(`Before "${methodName}"`);
    const result = target.call(this, ...args);
    console.log(`After "${methodName}"`);
    return result;
  }

  return replacementMethod;
}