属性装饰器

function Override(label: string) {
  return function (target: any, key: string) {
    Object.defineProperty(target, key, { 
      configurable: false,
      get: () => label
    });
  }
}
class Test {
  @Override('test')      // invokes Override, which returns the decorator
  name: string = 'pat';
}
let t = new Test();
console.log(t.name);  // 'test'

function ReadOnly(target: any, key: string) {
  Object.defineProperty(target, key, { writable: false });
}
class Test {
  @ReadOnly             // notice there are no `()`
  name: string;
}
const t = new Test();
t.name = 'jan';     
console.log(t.name); // 'undefined'