JavaScript

Requirements

• Node.js 20.x LTS ke atas — cek nodejs.org
• npm (sudah include di instalasi Node.js)

node --version && npm --version

Variabel & Tipe

const name = "SaidQB";           // tidak bisa di-reassign
let age = 8, active = true;      // bisa di-reassign
var legacy = "hindari var";      // function-scoped, sebaiknya dihindari

const tags = ["js", "go", "php"];
const config = { debug: true, port: 8000 };

`Halo ${name}, umur ${age} tahun`            // template literal
typeof age; Array.isArray(tags);

Function & Arrow Function

function greet(name, greeting = "Halo") {
  return `${greeting}, ${name}!`;
}

const square = (x) => x * x;
const total = (...args) => args.reduce((a, b) => a + b, 0);   // rest params

Array Methods

tags.map((t) => t.toUpperCase());
tags.filter((t) => t.length > 2);
tags.reduce((acc, t) => acc + t, "");
tags.find((t) => t === "go");
tags.some((t) => t === "js"); tags.every((t) => t.length > 0);
tags.includes("php");
[...tags].sort(); [...tags].reverse();       // spread biar tidak mutate array asli

Object & Destructuring

const { name, age } = user;                  // object destructuring
const [first, ...rest] = tags;               // array destructuring
const merged = { ...config, timeout: 30 };   // spread merge
Object.keys(config); Object.values(config); Object.entries(config);

Async, Promise, Fetch

async function getUser(id) {
  const res = await fetch(`/api/users/${id}`);
  if (!res.ok) throw new Error("Gagal fetch");
  return res.json();
}

getUser(1).then((u) => console.log(u)).catch((e) => console.error(e));

Promise.all([getUser(1), getUser(2)]);       // jalan paralel

Class

class User {
  constructor(name, email) {
    this.name = name;
    this.email = email;
  }
  greet() {
    return `Halo, saya ${this.name}`;
  }
}

class Admin extends User {
  constructor(name, email) {
    super(name, email);
  }
}

Module (ESM)

export function add(a, b) { return a + b; }
export default class User {}

import User, { add } from "./user.js";
import * as utils from "./utils.js";