['a', 'b', 'c'].includes('a') // true

let num = 2;

Math.pow(num, 10); // 1024
2 ** 10; // 1024

num **= 10;
num; // 1024

padStart(targetLength [, padString])
padEnd(targetLength [, padString])

`1월`.padStart(1);        // "1월"
`1월`.padStart(3);        // " 1월"
`1월`.padStart(3, "0");   // "01월"
`1월`.padStart(7, "0AB"); // "0AB0A1월"

const obj1 = {name: "Jhon", age: 24};
Object.values(obj1); // ["Jhon", 24]

const obj1 = {name: "Jhon", age: 24};

Object.keys(obj1);    // ["name", "age"]
Object.values(obj1);  // ["Jhon", 24]

Object.entries(obj1); // [["name", "Jhone"], ["age", 24]]

Object.getOwnPropertyDescriptor(obj, prop)

Object.getOwnPropertyDescriptor(obj)

console.log(Object.getOwnPropertyDescriptor(obj1, "name"));
// Object {value: "Jhon", writable: true, enumerable: true, configurable: true}

console.log(Object.getOwnPropertyDescriptors(obj1));
// Object {
//   name: {value: "Jhon", writable: true, enumerable: true, configurable: true}, 
//   age: {value: 24, writable: true, enumerable: true, configurable: true}
// }

const foo = (a, b, c,) => {}

// Rest
const { one, two, ...others } = { one: 1, two: 2, three: 3, four: 4, five: 5 }
console.log(one, two, others); // 1 2 {three: 3, four: 4, five: 5}

// Spread
const obj1 = {one, two, ... others};
console.log(obj); // {one: 1, two: 2, three: 3, four: 4, five: 5}

const obj2 = { one: 100, five: 500 };
const obj3 = { five: 5000 };
const obj = { ...obj1, ...obj2, ...obj3};
console.log(obj); // {one: 100, two: 2, three: 3, four: 4, five: 5000}

Promise.resolve('reslove')
.then((res) => console.log('success'))
.catch((err) => console.log('fail'))
.finally(() => console.log('finally'))

for await (const req of requests) {
console.log(req)
}

const s = "     hello world";
const e = "!     ";

console.log(s + e + ';');
// "     hello world!     ;"

console.log(s.trimStart() + e.trimEnd() + ';');
// "hello world!;"

try {
// some code
}
catch (err) {
// error handling code
}

try {
// some code
}
catch {
// error handling code
}

const obj1 = {name: "Jhon", age: 24};

const entries = Object.entries(obj1); 
console.log(entries); // [["name", "Jhone"], ["age", 24]]

const fromEntries = Object.fromEntries(entries);
console.log(fromEntries); // {name: "Jhon", age: 24}

const arr = [1, , 2, [3, 4, [5, 6]]];

console.log(arr.flat());  // [1, 2, 3, 4, [5, 6]]
console.log(arr.flat(1)); // [1, 2, 3, 4, [5, 6]]

console.log(arr.flat(2)); // [1, 2, 3, 4, 5, 6]

const arr = [1,2,3];

const map = arr.map(v => [v]);
const flatMap = arr.flatMap(v=> [v]);

console.log(map);         // [[1], [2], [3]]
console.log(map.flat());  // [1, 2, 3]

console.log(flatMap);     // [1, 2, 3]

import config from './config.js';

if(response) {
age = config.age;
}

if(response) {
import('./config.js')
.then(config => {
  age = config.age;
  console.log(config);
}
}

export const age = 24;

export const skills = ["react", "webpack"];

export default "Jhon";

const int1 = Number.MAX_SAFE_INTEGER + 1; 
// 9007199254740992

const int2 = Number.MAX_SAFE_INTEGER + 2; 
// 9007199254740992  <= ~993이 아니다.

const bigInt2 = BigInt(Number.MAX_SAFE_INTEGER) + 2n; 
// 9007199254740993n <= ~993이 되었다.

console.log(typeof int1, typeof int2, typeof bigInt2); 
// number number bigint

console.log(typeof 9007199254740993n); // bigint
console.log(9007199254740993n === bigInt2); // true
// 일반적인 숫자 뒤에 n을 붙이는 것으로 bitint 타입을 가진다는 것을 알 수 있습니다.

console.log(BigInt(10), BigInt(10n));
// 10n 10n <= BitInt의 인자로는 n의 여부가 중요하지 않다.

console.log(10 === BigInt(10)); // false
console.log(10 == BigInt(10)); // true

// console.log(9007199254740993n + 1);
// 위 코드는 에러가 발생한다. bigint를 연산할때는 number 타입과 섞어쓰는 것이 안된다.

const p1 = new Promise((resolve, reject) => resolve("p1, resolved"));
const p2 = new Promise((resolve, reject) => resolve("p2, resolved"));
const p3 = new Promise((resolve, reject) => reject("p3, rejected"));

Promise.all([p1, p2, p3])
.then(response => console.log(response))
.catch(err => {
console.log(err);
});
/*
console.log(response)
{status: "fulfilled", value: "p1, resolved"}
{status: "fulfilled", value: "p2, resolved"}
{status: "rejected", reason: "p3, rejected"}
*/

Promise.allSettled([p1, p2, p3])
.then(response => console.log(response))
.catch(err => {
console.log(err);
});
/*
console.log(err);
p3, rejected
*/

0 || 'A'    // A
0 ?? 'A'    // 0

0 ? 0 : 'A' // A
0 ?? 'A'    // 0

const foo = {
a: {
b: true
}
};

console.log(foo.a.b); // true
console.log(foo.b?.b); // undefined

console.log(foo.b.aa); // TypeError: Cannot read property 'aa' of undefined