JavaScript属性描述符_javascript对象特性

const obj = { name: 'Alice' };
console.log(Object.getOwnPropertyDescriptor(obj, 'name'));
// 输出：
// {
//   value: 'Alice',
//   writable: true,
//   enumerable: true,
//   configurable: true
// }

const person = {};
Object.defineProperty(person, 'age', {
  value: 25,
  writable: false,      // 不可修改
  enumerable: true,     // 可枚举
  configurable: false   // 不可删除或重新配置
});

person.age = 30;
console.log(person.age); // 仍然输出 25

const book = {
  _title: 'JavaScript Guide'
};

Object.defineProperty(book, 'title', {
  get() {
    return this._title.toUpperCase();
  },
  set(value) {
    if (value.length > 0) {
      this._title = value;
    }
  },
  enumerable: true,
  configurable: true
});

console.log(book.title); // "JAVASCRIPT GUIDE"
book.title = 'Learning JS';
console.log(book.title); // "LEARNING JS"

const user = {};

Object.defineProperties(user, {
  firstName: {
    value: 'John',
    writable: false
  },
  lastName: {
    value: 'Doe',
    writable: true
  },
  fullName: {
    get() {
      return this.firstName + ' ' + this.lastName;
    }
  }
});

Object.defineProperty(obj, 'prop', {
  value: 10,
  configurable: false
});

// 下面这行会报错
Object.defineProperty(obj, 'prop', { enumerable: true });