script.js

// alert from external JavaScript file
// alert('I am an external JavaScript');

// splitting code into two alerts
// alert('Hello');
// alert('World');

// storing values in variables
let greeting = 'Hello, World!'; // greeting is the variable while 'Hello, World!' is the string value stored in it
// alert(greeting);  // displays the value stored in the variable greeting

// let user = 'John',
//   age = 25,                        this is another way of declaring multiple variables 
//   message = 'Hello';
// let user = 'John', age = 25, message = 'Hello';     // or you can write it in a single line
// When the stored string value is changed, the old data is forgotten from the variable even though it's still present in the code.

//  declare two variables and copy data from one into the other.
// let hello = 'Hello world!';
// let message;
// message = hello;
// alert(hello); // Hello world!
// alert(message); // Hello world!

// note: no "use strict" in this example
num = 5; // the variable "num" is created if it didn't exist
// alert(num); // 5

// When the name contains multiple words, camelCase is used.
// That is: each word except first starting with a capital letter: myVeryLongName.
// const pageLoadTime has a different value each time the webpage reloads but it's constant after the page is loaded.

// let admin, name;
// name = "John";
// admin = name;
// alert(admin);

// Create a variable with the name of our planet. How would you name such a variable?
// Create a variable to store the name of a current visitor to a website. How would you name that variable?

let thirdPlanet = 'earth';
let currentVisitor= 'John';

// alert(`Hello, ${currentVisitor}! Welcome to ${thirdPlanet}.`);
// Backticks
// alert(`There were ${1 + 2} of them`)
// console.log(`There were ${1 + 2} of them`)

// Boolean
// let isBigger = 4 > 1;
// let isSmaller = 4 < 1;
// alert(isBigger); // true
// alert(isSmaller); // false
// console.log(isBigger); // true
// console.log(isSmaller); // false

// Null (nothing)
// let age = null;
// console.log(age);
// alert(age); // null

// Undefined means "value is not assigned"
// let age1;
// console.log(age1);
// alert(age1); // undefined

// Typeof
console.log(typeof '1234'); // "string"
console.log(typeof 1234);   // "number"
console.log(typeof Math);  // "object"
console.log(typeof alert); // "function"
console.log(typeof true);   // "boolean"
console.log(typeof undefined); // "undefined"
console.log(typeof null);    // "object" (this is a historical bug in JavaScript)

// prompt 
// prompt('Name:', 'Enter your name here');
// let userEmail = prompt('Enter your email:','email@example.com');
// alert(`Your email "${userEmail}" has been accepted.`);

// confirm
// let isAdult = confirm('Are you 18 years old or older?');
// alert(isAdult); // true if OK is pressed