JavaScriptのデストラクチャリングで変数の割り当てを効率化

// 配列のデストラクチャリング
const numbers = [1, 2, 3];
const [first, second] = numbers;
console.log(first); // 1
console.log(second); // 2

// オブジェクトのデストラクチャリング
const person = { name: 'Alice', age: 25 };
const { name, age } = person;
console.log(name); // Alice
console.log(age); // 25

// 配列のデフォルト値
const [a = 10, b = 20] = [5];
console.log(a); // 5
console.log(b); // 20

// オブジェクトのデフォルト値
const { x = 100, y = 200 } = { x: 50 };
console.log(x); // 50
console.log(y); // 200

// 配列で残りの値をまとめる
const [head, ...tail] = [1, 2, 3, 4];
console.log(head); // 1
console.log(tail); // [2, 3, 4]

// オブジェクトで残りのプロパティをまとめる
const { name, ...rest } = { name: 'Alice', age: 25, city: 'New York' };
console.log(name); // Alice
console.log(rest); // { age: 25, city: 'New York' }

const { name: fullName, age: yearsOld } = { name: 'Alice', age: 25 };
console.log(fullName); // Alice
console.log(yearsOld); // 25

const person = {
  name: 'Alice',
  address: {
    city: 'New York',
    postalCode: '10001'
  }
};

const { name, address: { city, postalCode } } = person;
console.log(name); // Alice
console.log(city); // New York
console.log(postalCode); // 10001

function greet({ name, age }) {
  console.log(`Hello, ${name}. You are ${age} years old.`);
}

const person = { name: 'Alice', age: 25 };
greet(person); // Hello, Alice. You are 25 years old.

function createUser({ name = 'Guest', age = 18 } = {}) {
  console.log(`Name: ${name}, Age: ${age}`);
}

createUser(); // Name: Guest, Age: 18
createUser({ name: 'Alice' }); // Name: Alice, Age: 18
createUser({ name: 'Bob', age: 25 }); // Name: Bob, Age: 25

const [first, , third] = [1, 2, 3];
console.log(first); // 1
console.log(third); // 3

const [a, b, c] = [10, 20, 30];
console.log(a); // 10
console.log(b); // 20
console.log(c); // 30

const arr = [1, 2, 3, 4];
const [first, second, ...rest] = arr;
console.log(first); // 1
console.log(second); // 2
console.log(rest); // [3, 4]

const person = null;

const { name, age } = person || {};
console.log(name); // undefined
console.log(age); // undefined