First JS live class with AltSchool v4 student

intro.js

// variables and data types - number, string, boolean, null , undefined
// var, let, const

// declare a variable (identifier)
// var name;
let principal = 'Adedeji'; // string `, ", '
// interpolation - ${}
let address = `
  1, Oluwaseyi Street,
  Ojodu Berger,
`

let age = 20; // number

//
let isStudent = true; // boolean
let notAStudent = !isStudent
// assign a value to a variable
// name = "John";

// null - nothing|empty or undefined (i do not have a value)
let country = null;
let letterO = 'O';
let zero = 0;
console.log(typeof letterO)


// undefined - not defined
let state;

console.log(state)

// truthy and falsy values
// evertything is truthy except falsy values
// falsy values - false, 0, "", null, undefined, NaN

let isOfAge = 18;

const COST_PRICE = 3.142;

// COST_PRICE = 3.14;
// Assignment operators
// Please assign the value of 20 to isOfAge
isOfAge = 20;

// Arithmetic operators - +, -, * , /, %(reminder division - modulo), ++(increment), -- (decrement), ** (exponentiation)

5 % 2  // 1

// % -modulo - differentiate between even and odd numbers
2 % 2 == 0 // even
3 % 2 == 1 // odd

console.log(5 - 2)
console.log(5 + 2)
console.log(5 * 2)
console.log(5 / 2)

// 5 raised to the power of 2
console.log(5 ** 2)
console.log(5 ** 3)


// ++increment++ and --decrement-- - pre and post
let count = 0;

// pre-increment
console.log(++count) // 1
console.log(++count) // 2
console.log(++count) // 2
console.log(count)
console.log(count++) //
console.log(count)


count // 4

--count
--count
--count
count
count--
count

// BigInt
let bigNumber = 10n;

// Summary - pre of (increment | decrement) - increment first before using the value
// post of (increment | decrement) - use the value first before incrementing or decrementing

// Comparison operators - ==, ===, !=, !==, >, <, >=, <=
// = assignment operator
// == // equality operator - checks the value only
// === // strict equality operator - checks the value and the data type

// != // not equal to
// !== // strict not equal to

console.log(2 > 3)
console.log(age >= 18)
console.log(2 < 3);

console.log(2 == '2');
console.log(2 === '2')
// == - equality operator - checks the value


// semicolon
// ASI - Automatic Semicolon Insertion
// 1. when the line ends