JavaScript

// JavaScript cheat-sheet
// Single-line comment
/* multi-line */

let x = 10;             // mutable
const PI = 3.14;        // immutable binding
var legacy = 1;         // avoid in modern code

// Strings
const name = "ada";
const greet = `Hello, ${name}!`;   // template literal

// Arrays / objects
const nums = [1, 2, 3];
nums.push(4);
const person = { name: "ada", age: 36 };

// Conditions
if (x > 0) {
  console.log("positive");
} else if (x === 0) {
  console.log("zero");
} else {
  console.log("negative");
}

// Loops
for (let i = 0; i < 5; i++) console.log(i);
for (const n of nums) console.log(n);

// Functions
function add(a, b) { return a + b; }
const mul = (a, b) => a * b;

// Higher-order
nums.map(n => n * 2);
nums.filter(n => n > 1);
nums.reduce((a, b) => a + b, 0);

// Destructuring & spread
const { name: n1 } = person;
const more = [...nums, 5, 6];

// Classes
class Animal {
  constructor(name) { this.name = name; }
  greet() { return `hi, ${this.name}`; }
}