JavaScript 数组和对象

// 字面量语法
const fruits = ['apple', 'banana', 'orange'];

// Array 构造函数
const numbers = new Array(1, 2, 3, 4, 5);

// Array.from() 方法
const characters = Array.from('Hello'); // ['H', 'e', 'l', 'l', 'o']

const colors = ['red', 'green', 'blue'];

// 访问元素
console.log(colors[0]);     // 'red'
console.log(colors.length); // 3

// 修改元素
colors[1] = 'yellow';
console.log(colors); // ['red', 'yellow', 'blue']

const numbers = [1, 2, 3, 4, 5];

// 添加和删除元素
numbers.push(6);         // 末尾添加
numbers.unshift(0);      // 开头添加
numbers.pop();           // 删除末尾元素
numbers.shift();         // 删除开头元素

// 查找元素
const index = numbers.indexOf(3);     // 返回元素索引
const found = numbers.includes(4);    // 检查元素是否存在

// 数组转换
const joined = numbers.join(', ');    // 转换为字符串
const sliced = numbers.slice(1, 4);   // 截取部分数组
const reversed = numbers.reverse();    // 反转数组

const fruits = ['apple', 'banana', 'orange'];

// forEach 方法
fruits.forEach((fruit, index) => {
    console.log(`${index}: ${fruit}`);
});

// map 方法
const upperFruits = fruits.map(fruit => fruit.toUpperCase());

// filter 方法
const longFruits = fruits.filter(fruit => fruit.length > 5);

// reduce 方法
const letters = fruits.reduce((total, fruit) => total + fruit.length, 0);

// 字面量语法
const person = {
    name: 'Alice',
    age: 25,
    sayHello() {
        console.log('Hello!');
    }
};

// 构造函数
function Person(name, age) {
    this.name = name;
    this.age = age;
}
const bob = new Person('Bob', 30);

const user = {
    name: 'Alice',
    age: 25,
    address: {
        city: 'Beijing',
        street: 'Main St'
    }
};

// 点号访问
console.log(user.name);           // 'Alice'
console.log(user.address.city);   // 'Beijing'

// 方括号访问
console.log(user['age']);         // 25

// 添加新属性
user.email = '[email protected]';

// 删除属性
delete user.age;

const book = {
    title: 'JavaScript Guide',
    price: 29.99
};

// 获取所有键
console.log(Object.keys(book));     // ['title', 'price']

// 获取所有值
console.log(Object.values(book));   // ['JavaScript Guide', 29.99]

// 获取所有键值对
console.log(Object.entries(book));  // [['title', 'JavaScript Guide'], ['price', 29.99]]

// 合并对象
const details = { author: 'John Doe' };
const fullBook = Object.assign({}, book, details);
// 或使用展开运算符
const newBook = { ...book, ...details };

const numbers = [1, 2, 3, 4, 5];

// 基本解构
const [first, second] = numbers;
console.log(first, second);  // 1, 2

// 跳过元素
const [, , third] = numbers;
console.log(third);  // 3

// 剩余元素
const [head, ...tail] = numbers;
console.log(head, tail);  // 1, [2, 3, 4, 5]

const person = {
    name: 'Alice',
    age: 25,
    city: 'Beijing'
};

// 基本解构
const { name, age } = person;
console.log(name, age);  // 'Alice', 25

// 重命名
const { name: fullName, age: years } = person;
console.log(fullName, years);  // 'Alice', 25

// 默认值
const { country = 'China' } = person;
console.log(country);  // 'China'