text: function readonly(target, name, descriptor) {
    descriptor.writable = false;
    return descriptor;
  }
  
  class Example {
    a() {}
    @readonly
    b() {}
  }
  
  const e = new Example();
  e.a = 1;
  e.b = 2;
  // TypeError: Cannot assign to read only property 'b' of object '#<Example>'
  