JavaScript中根据条件动态创建对象属性的策略与实践

/**
 * 示例1: 基于全局变量的条件属性
 */
let enableFeatureA = true; // 模拟外部条件

function MyObjectWithCondition() {
    this.commonProp = "Always present";
    if (enableFeatureA) {
        this.featureAProp = "Value for Feature A";
    }
}

const obj1 = new MyObjectWithCondition();
console.log(obj1);
// 输出: { commonProp: 'Always present', featureAProp: 'Value for Feature A' }

enableFeatureA = false; // 改变条件
const obj2 = new MyObjectWithCondition();
console.log(obj2);
// 输出: { commonProp: 'Always present' }

/**
 * 示例2: 基于传入参数的条件属性
 */
function UserProfile(name, age) {
    this.name = name;
    if (age !== undefined && age !== null) { // 检查age是否提供
        this.age = age;
    }
    this.timestamp = new Date().toISOString();
}

const user1 = new UserProfile('Alice', 30);
console.log(user1);
// 输出: { name: 'Alice', age: 30, timestamp: '...' }

const user2 = new UserProfile('Bob'); // 未提供age
console.log(user2);
// 输出: { name: 'Bob', timestamp: '...' }

const someCondition = true;
const anotherCondition = false;

const myObject = {
    fixedProp: 'This is always here',
    // 如果 someCondition 为 true，则展开 { conditionalPropA: 'Value A' }
    // 否则展开一个空对象 {}
    ...(someCondition ? { conditionalPropA: 'Value A' } : {}),
    // 也可以链式添加多个条件属性
    ...(anotherCondition ? { conditionalPropB: 'Value B' } : {}),
    lastProp: 'Another fixed property'
};

console.log(myObject);
// 输出: { fixedProp: 'This is always here', conditionalPropA: 'Value A', lastProp: 'Another fixed property' }

// 改变条件
const someConditionFalse = false;
const myObject2 = {
    fixedProp: 'This is always here',
    ...(someConditionFalse ? { conditionalPropA: 'Value A' } : {}),
    lastProp: 'Another fixed property'
};
console.log(myObject2);
// 输出: { fixedProp: 'This is always here', lastProp: 'Another fixed property' }

const userRole = 'admin';
const userStatus = 'active';

// 使用 IIFE
const userConfig = (() => {
    const config = {
        id: 'user_123',
        username: 'john.doe',
        email: 'john.doe@example.com'
    };

    if (userRole === 'admin') {
        config.isAdmin = true;
        config.permissions = ['read', 'write', 'delete'];
    } else {
        config.isAdmin = false;
        config.permissions = ['read'];
    }

    if (userStatus === 'active') {
        config.isActive = true;
    } else {
        config.isActive = false;
        config.deactivationReason = 'inactive';
    }

    return config;
})();

console.log(userConfig);
/*
输出:
{
  id: 'user_123',
  username: 'john.doe',
  email: 'john.doe@example.com',
  isAdmin: true,
  permissions: [ 'read', 'write', 'delete' ],
  isActive: true
}
*/

// 使用辅助函数
function createProductConfig(productId, isAvailable, hasDiscount) {
    const config = {
        productId: productId,
        category: 'electronics'
    };

    if (isAvailable) {
        config.status = 'in_stock';
        config.deliveryTime = '2-3 days';
    } else {
        config.status = 'out_of_stock';
    }

    if (hasDiscount) {
        config.discountRate = 0.15;
        config.originalPrice = 100; // 假设
        config.finalPrice = config.originalPrice * (1 - config.discountRate);
    }

    return config;
}

const product1 = createProductConfig('P001', true, true);
console.log(product1);
const product2 = createProductConfig('P002', false, false);
console.log(product2);

const userLoggedIn = true;
const userHasPremium = false;

// 使用 if 语句
const userData = {
    id: 456,
    username: 'jane.doe',
    email: 'jane.doe@example.com'
};

if (userLoggedIn) {
    userData.lastLogin = new Date().toISOString();
}

if (userHasPremium) {
    userData.subscriptionTier = 'premium';
    userData.adFree = true;
}

console.log(userData);
/*
输出:
{
  id: 456,
  username: 'jane.doe',
  email: 'jane.doe@example.com',
  lastLogin: '2023-10-27T...' // 实际时间
}
*/

// 使用 Object.defineProperty (通常用于更高级的属性控制，如不可枚举、不可配置等)
const configObject = {
    appName: 'My App'
};
const enableDebugMode = true;

if (enableDebugMode) {
    Object.defineProperty(configObject, 'debugMode', {
        value: true,
        writable: false, // 示例：不可修改
        enumerable: true, // 示例：可枚举
        configurable: false // 示例：不可配置
    });
}

console.log(configObject);
// 输出: { appName: 'My App', debugMode: true }