const variableNames: string; // camelCase
const CONSTANT_VAR = "value"; // UPPERCASE
 
class ClassName {} // PascalCase

let x = 5;
const y = 10;
 
x = 10; // valid
y = 20; // error

const name: string = "Alice";
const age: number = 25;
const height: number = 5.5;
const isTrue: boolean = true;
const fruits: string[] = ["apple", "banana"]; // array
const person: { name: string; age: number } = { name: "Alice", age: 25 }; // object

const x = 5;
console.log(typeof x); // number

const fruits: string[] = ["apple", "banana"];
fruits[0]; // get
fruits.push("cherry"); // add
fruits.slice(1, 1); // remove
 
for (const fruit of fruits) {
  console.log(fruit);
}

interface Person: {
  name: string;
  age: number;
}
 
const person: Person = { name: "Alice", age: 25 };
person.name; // get
 
for (const key in person) {
  console.log(key, person[key]);
}

const username = "Alex";
console.log("Welcome " + username); // Welcome Alex
 
const name = "Bob";
console.log(`Thanks ${name}`); // Thanks Bob

const name = prompt("Name: ");
const height = Number(prompt("Height: "));

if (temperature > 25) {
  console.log("Hot!");
} else if (temperature < 0) {
  console.log("Cold!");
} else {
  console.log("Mild");
}

const fruits = ["apple", "banana", "cherry"];
for (const fruit of fruits) {
  console.log(fruit);
}
 
for (const i = 0; i <= 5; i++) {
  console.log(i); // 0, 1, 2, 3, 4, 5
}
 
fruits.forEach((fruit, index) => {
  console.log(index, fruit);
});

while (condition) {
  console.log("condition is True");
}

for (let i = 0; i < 10; i++) {
  if (i === 5) break;
  console.log(i); // 0, 1, 2, 3, 4
}
 
for (let i = 0; i < 5; i++) {
  if (i === 2) continue;
  console.log(i); // 0, 1, 3, 4
}

==  // equal
=== // equal value and type
!=  // not equal
>   // greater than
<   // less than
>=  // greater or equal
<=  // less or equal

if (x > 0 && x < 10) {
  console.log("x is between 0 and 10");
}
 
if (x < 0 || x > 10) {
  console.log("Outside range");
}
 
const isValid = !false;

function add(a: number, b: number): number {
  return a + b;
}
 
const result = add(5, 3);
console.log(result); // 8

// positional args
function area(width: number, height: number): number {
  return width * height;
}
 
area(5, 6);
 
// default args
function areaWithDefaults(width = 5, height = 5): number {
  return width * height;
}
 
areaWithDefaults(); // uses default values
 
// rest args
function areaWithRest(...args: number[]): number {
  return args[0] * args[1];
}
 
areaWithRest(5, 6);

"Hello".length; // length
typeof 123; // type check
parseInt("42"); // convert to int
String(123); // convert to string
Math.round(3.14159); // round

const x = 10; // global var
const whatScope = "global";
 
function outer() {
  const y = 20; // function scope
  const whatScope = "function";
 
  function inner() {
    const z = 30; // block scope
    const whatScope = "block";
    console.log(x, y, z); // can access all higher scopes
    console.log(whatScope); // block
  }
 
  inner();
  console.log(x, y); // z doesn't exist here
  console.log(whatScope); // function
}
 
outer();
console.log(x); // y and z don't exist globally
console.log(whatScope); // global

import { sqrt } from "mathjs"; // import a function
import * as _ from "lodash"; // import all functions

try {
  throw new Error("Error!");
} catch (e) {
  console.log(e.message);
}

import { readFileSync, writeFileSync } from "fs";
 
const content = readFileSync("file.txt", "utf-8");
console.log(content);
 
writeFileSync("file.txt", "Hello, world!");