🟨 JavaScript Cheatsheet

let x = 42;             // mutable
const PI = 3.14;        // immutable binding
// Don't use var in modern code

const name = 'Aisha';
`Hello, ${name}`        // template literal
name.toUpperCase()
name.toLowerCase()
name.includes('isha')
name.replace('A', 'B')
name.split(',')
['a','b'].join(',')
name.trim()

const xs = [1, 2, 3];
xs.push(4);             // [1,2,3,4]
xs.pop();
xs[0]; xs.at(-1);
xs.length
xs.slice(1, 3)
xs.map(n => n * 2)
xs.filter(n => n > 1)
xs.reduce((a, b) => a + b, 0)
xs.find(n => n > 2)
[...xs]                  // shallow copy

const user = { name: 'Aisha', age: 30 };
user.name; user['age'];
user.role = 'admin';
Object.keys(user); Object.values(user); Object.entries(user);
'age' in user
delete user.age;
const { name, age } = user;     // destructure
const copy = { ...user };       // shallow copy

if (cond) { ... } else if (cond2) { ... } else { ... }

// Ternary
const status = age >= 18 ? 'adult' : 'minor';

// Switch
switch (day) {
  case 'Sat':
  case 'Sun': console.log('weekend'); break;
  default: console.log('weekday');
}

for (let i = 0; i < 5; i++) { ... }
for (const x of xs) { ... }
for (const k in obj) { ... }
while (cond) { ... }
xs.forEach((x, i) => { ... });

function greet(name, greeting = 'Hello') {
  return `${greeting}, ${name}!`;
}

const greet = (name) => `Hello, ${name}!`;

// Rest / spread
function sum(...nums) { return nums.reduce((a,b) => a+b, 0); }

async function getUser(id) {
  const r = await fetch(`/users/${id}`);
  return r.json();
}

try {
  const u = await getUser(1);
} catch (e) {
  console.error(e);
}

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

class Admin extends User { ... }
const u = new User('Aisha');