Cheat Sheet de JavaScript

const x = 10

let y = 20

typeof x

const { a, b } = obj

const [a, b] = arr

const merged = { ...obj1, ...obj2 }

const copy = [...arr]

x ?? fallback

obj?.prop?.nested

[1, 2, 3]

arr.push(item)

arr.pop()

arr.shift();
arr.unshift(item);

arr.map(x => x * 2)

arr.filter(x => x > 0)

arr.reduce((acc, x) => acc + x, 0)

arr.find(x => x.id === 1)

arr.findIndex(x => x > 5)

arr.some(x => x > 0)

arr.every(x => x > 0)

arr.includes(item)

arr.flat(Infinity)

const numbers = [10, 2, 1];
const sorted = [...numbers].sort((a, b) => a - b);
console.log(sorted); // [1, 2, 10]
console.log(numbers); // [10, 2, 1]

arr.slice(1, 3)

arr.splice(1, 2, ...items)

[...new Set(arr)]

Array.from({ length: 5 }, (_, i) => i)

const obj = { key: "value" }

Object.keys(obj)

Object.values(obj)

Object.entries(obj)

Object.assign({}, obj1, obj2)

structuredClone(obj)

Object.freeze(obj)

"key" in obj

delete obj.key

const { unwanted, ...rest } = obj

function fn(x) { return x }

const fn = (x) => x * 2

const fn = (x = 10) => x

const fn = (...args) => args

fn(1, ...arr)

setTimeout(fn, 1000)

setInterval(fn, 1000)

function* gen() { yield 1 }

async function fetchJson(url) {
  const res = await fetch(url);
  if (!res.ok) throw new Error(`HTTP ${res.status}`);
  return res.json();
}

fetch(url)
  .then(r => {
    if (!r.ok) throw new Error(`HTTP ${r.status}`);
    return r.json();
  })
  .then(console.log)
  .catch(console.error);

Promise.all([p1, p2])

Promise.race([p1, p2])

Promise.allSettled([p1, p2])

const promise = new Promise(resolve => {
  setTimeout(() => resolve(42), 100);
});
promise.then(console.log); // 42

try {
  await fn();
} catch (e) {
  console.error(e);
}

`Hello ${name}`

s.includes("sub")

s.startsWith("pre");
s.endsWith("suf");

s.split(",")

s.trim()

s.replace(/regex/g, "new")

s.padStart(5, "0")

s.repeat(3)

s.match(/pattern/g)

s.at(-1)

document.querySelector(".class")

document.querySelectorAll("div")

el.addEventListener("click", fn)

el.classList.add("active")

el.classList.toggle("hidden")

el.textContent = "text"

el.setAttribute("data-id", "5")

el.style.color = "red"

el.remove()

const m = new Map()

const s = new Set([1, 2, 3])

for (const [k, v] of map) {}

for (const item of iterable) {}

Symbol("desc")

import { fn } from "./module.js"

export default fn

const proxy = new Proxy(target, handler)