Milan960
3 years ago
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<!DOCTYPE html>
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<html>
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<head>
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<title>Document Object Model:30 Days Of JavaScript</title>
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<link href="https://fonts.googleapis.com/css?family=Lato:300, 400,400i,700,700i&display=swap" rel="stylesheet">
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<link href="https://fonts.googleapis.com/css?family=Montserrat:300,400,500&display=swap" rel="stylesheet">
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</head>
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<body>
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<div class="wrapper">
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<h1>Asabeneh Yetayeh challenges in <span>2020</span></h1>
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<h2>30DaysOfJavaScript Challenge</h2>
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<p></p>
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<ul>
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<li>30DaysOfPython Challenge Done</li>
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<li>30DaysOfJavaScript Challenge Ongoing</li>
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<li>30DaysOfReact Challenge Coming</li>
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<li>30DaysOfReactNative Challenge Coming</li>
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<li>30DaysOfFullStack Challenge Coming</li>
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<li>30DaysOfDataAnalysis Challenge Coming</li>
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<li>30DaysOfMachineLearning Challenge Coming</li>
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</ul>
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</div>
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<script>
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const hexaColor = () => {
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const str = '0123456789abcdef'
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let hexa = '#'
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let index
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for (let i = 0; i < 6; i++) {
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index = Math.floor(Math.random() * str.length)
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hexa += str[index]
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}
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return hexa
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const showDateTime = () => {
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const months = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September',
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'October', 'November', 'December'
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]
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const now = new Date()
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const year = now.getFullYear()
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const month = months[now.getMonth()]
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const dateMonthYear = `${month} ${date}, ${year}`
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const time = hours + ':' + minutes
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const fullTime = dateMonthYear + ' ' + time
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return fullTime + `:${seconds}`
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}
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const wrapper = document.querySelector('.wrapper')
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const year = document.querySelector('span')
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const time = document.querySelector('p')
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wrapper.style.width = '50%'
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wrapper.style.margin = 'auto'
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const title = document.querySelector('h1')
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const subTitle = document.querySelector('h2')
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title.style.textAlign = 'center'
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title.style.fontFamily = 'Montserrat'
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title.style.fontWeight = 500
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subTitle.style.textAlign = 'center'
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subTitle.style.fontFamily = 'Montserrat'
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subTitle.style.fontWeight = 300
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subTitle.style.textDecoration = 'underline'
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time.style.textAlign = 'center'
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time.style.fontFamily = 'Montserrat'
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time.style.fontWeight = 400
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setInterval(() => {
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year.style.color = hexaColor()
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year.style.fontSize = '96px'
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year.style.fontWeight = 700;
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time.textContent = showDateTime()
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time.style.background = hexaColor()
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time.style.width = "25%"
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time.style.margin = 'auto'
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time.style.padding = '10px'
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}, 1000)
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const ul = document.querySelector('ul')
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const lists = document.querySelectorAll('li')
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for (const list of lists) {
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list.style.padding = '25px'
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list.style.margin = '3px'
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list.style.fontFamily = 'Montserrat'
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list.style.fontWeight = 300;
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list.style.letterSpacing = '0.0625em'
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if (list.textContent.includes('Done')) {
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list.style.background = '#21bf73'
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} else if (list.textContent.includes('Ongoing')) {
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list.style.background = '#fddb3a'
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} else {
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list.style.background = '#fd5e53'
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}
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}
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</script>
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</body>
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</html>
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@ -0,0 +1,674 @@
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# 30 Days Of JavaScript
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| # Day | Topics |
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| ----- | :-------------------------------------------------------------------------------------------------------------------------------------------------: |
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| 01 | [wprowadzenie](./readMe.md) |
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| 02 | [Typy danych](./02_Day_Data_types/02_day_data_types.md) |
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| 03 | [Boole'a, operatory, data](./03_Day_Booleans_operators_date/03_booleans_operators_date.md) |
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| 04 | [Warunkowe](./04_Day_Conditionals/04_day_conditionals.md) |
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| 05 | [Tablice](./05_Day_Arrays/05_day_arrays.md) |
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| 06 | [Pętle](./06_Day_Loops/06_day_loops.md) |
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| 07 | [Funkcje](./07_Day_Functions/07_day_functions.md) |
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| 08 | [Obiekty](./08_Day_Objects/08_day_objects.md) |
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| 09 | [Funkcje wyższego rzędu](./09_Day_Higher_order_functions/09_day_higher_order_functions.md) |
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| 10 | [Zestawy i mapy](./10_Day_Sets_and_Maps/10_day_Sets_and_Maps.md) |
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| 11 | [Destrukturyzacja i rozprzestrzenianie](./11_Day_Destructuring_and_spreading/11_day_destructuring_and_spreading.md) |
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| 12 | [Wyrażenia regularne](./12_Day_Regular_expressions/12_day_regular_expressions.md) |
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| 13 | [Metody obiektów konsoli](./13_Day_Console_object_methods/13_day_console_object_methods.md) |
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| 14 | [Obsługa błędów](./14_Day_Error_handling/14_day_error_handling.md) |
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| 15 | [Klasy](./15_Day_Classes/15_day_classes.md) |
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| 16 | [JSON](./16_Day_JSON/16_day_json.md) |
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| 17 | [Magazyny internetowe](./17_Day_Web_storages/17_day_web_storages.md) |
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| 18 | [Obietnice](./18_Day_Promises/18_day_promises.md) |
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| 19 | [Zamknięcie](./19_Day_Closures/19_day_closures.md) |
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| 20 | [Pisanie czystego kodu](./20_Day_Writing_clean_codes/20_day_writing_clean_codes.md) |
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| 21 | [DOM](./21_Day_DOM/21_day_dom.md) |
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| 22 | [Manipulowanie obiektem DOM](./22_Day_Manipulating_DOM_object/22_day_manipulating_DOM_object.md) |
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| 23 | [Słuchacze zdarzeń](./23_Day_Event_listeners/23_day_event_listeners.md) |
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| 24 | [Mini Projekt: Układ Słoneczny](./24_Day_Project_solar_system/24_day_project_solar_system.md) |
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| 25 | [Mini Projekt: Wizualizacja danych krajów świata 1](./25_Day_World_countries_data_visualization_1/25_day_world_countries_data_visualization_1.md) |
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| 26 | [Mini Projekt: Wizualizacja danych krajów świata 2](./26_Day_World_countries_data_visualization_2/26_day_world_countries_data_visualization_2.md) |
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| 27 | [Mini Projekt: Portfolio](./27_Day_Mini_project_portfolio/27_day_mini_project_portfolio.md) |
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| 28 | [Mini projekt: Tablica wyników](./28_Day_Mini_project_leaderboard/28_day_mini_project_leaderboard.md) |
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| 29 | [Mini Projekt: animowane postacie](./29_Day_Mini_project_animating_characters/29_day_mini_project_animating_characters.md) |
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| 30 | [Projekty końcowe](./30_Day_Mini_project_final/30_day_mini_project_final.md) |
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🧡🧡🧡 HAPPY CODING 🧡🧡🧡
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<div>
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<small>Support the <strong>author</strong> to create more educational materials</small> <br />
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<a href = "https://www.paypal.me/asabeneh"><img src='./images/paypal_lg.png' alt='Paypal Logo' style="width:10%"/></a>
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</div>
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<div align="center">
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<h1> 30 Days Of JavaScript: Introduction</h1>
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<a class="header-badge" target="_blank" href="https://www.linkedin.com/in/asabeneh/">
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<img src="https://img.shields.io/badge/style--5eba00.svg?label=LinkedIn&logo=linkedin&style=social">
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</a>
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<a class="header-badge" target="_blank" href="https://twitter.com/Asabeneh">
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<img alt="Twitter Follow" src="https://img.shields.io/twitter/follow/asabeneh?style=social">
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</a>
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<sub>Author:
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<a href="https://www.linkedin.com/in/asabeneh/" target="_blank">Asabeneh Yetayeh</a><br>
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<small> January, 2020</small>
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</sub>
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<div>
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🇬🇧 [English](./readMe.md)
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🇪🇸 [Spanish](./Spanish/readme.md)
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🇷🇺 [Russian](./RU/README.md)
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🇦🇿 [Azerbaijan](./Azerbaijani/readMe.md)
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KR [Korean](./Korea/README.md)
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🇻🇳 [Vietnamese](./Vietnamese/README.md)
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</div>
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</div>
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</div>
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[Day 2 >>](./02_Day_Data_types/02_day_data_types.md)
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- [30 Days Of JavaScript](#30-days-of-javascript)
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- [📔 Day 1](#-day-1)
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- [Introduction](#introduction)
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- [Requirements](#requirements)
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- [Setup](#setup)
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- [Install Node.js](#install-nodejs)
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- [Browser](#browser)
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- [Installing Google Chrome](#installing-google-chrome)
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- [Opening Google Chrome Console](#opening-google-chrome-console)
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- [Writing Code on Browser Console](#writing-code-on-browser-console)
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- [Console.log](#consolelog)
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- [Console.log with Multiple Arguments](#consolelog-with-multiple-arguments)
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- [Comments](#comments)
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- [Syntax](#syntax)
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- [Arithmetics](#arithmetics)
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- [Code Editor](#code-editor)
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- [Installing Visual Studio Code](#installing-visual-studio-code)
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- [How to Use Visual Studio Code](#how-to-use-visual-studio-code)
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- [Adding JavaScript to a Web Page](#adding-javascript-to-a-web-page)
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- [Inline Script](#inline-script)
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- [Internal Script](#internal-script)
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- [External Script](#external-script)
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- [Multiple External Scripts](#multiple-external-scripts)
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- [Introduction to Data types](#introduction-to-data-types)
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- [Numbers](#numbers)
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- [Strings](#strings)
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- [Booleans](#booleans)
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- [Undefined](#undefined)
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- [Null](#null)
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- [Checking Data Types](#checking-data-types)
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- [Comments Again](#comments-again)
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- [Variables](#variables)
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- [💻 Day 1: Exercises](#-day-1-exercises)
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# 📔 Day 1
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## Introduction
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**Congratulations** on deciding to participate in 30 days of JavaScript programming challenge. In this challenge you will learn everything you need to be a JavaScript programmer, and in general, the whole concept of programming. In the end of the challenge you will get a 30DaysOfJavaScript programming challenge completion certificate. In case you need help or if you would like to help others you may join the [telegram group](https://t.me/ThirtyDaysOfJavaScript).
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**A 30DaysOfJavaScript** challenge is a guide for both beginners and advanced JavaScript developers. Welcome to JavaScript. JavaScript is the language of the web. I enjoy using and teaching JavaScript and I hope you will do so too.
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In this step by step JavaScript challenge, you will learn JavaScript, the most popular programming language in the history of mankind.
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JavaScript is used **_to add interactivity to websites, to develop mobile apps, desktop applications, games_** and nowadays JavaScript can be used for **_machine learning_** and **_AI_**.
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**_JavaScript (JS)_** has increased in popularity in recent years and has been the leading
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programming language for six consecutive years and is the most used programming language on
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Github.
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## Requirements
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No prior knowledge of programming is required to follow this challenge. You need only:
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1. Motivation
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2. A computer
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3. Internet
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4. A browser
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5. A code editor
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## Setup
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I believe you have the motivation and a strong desire to be a developer, a computer and Internet. If you have those, then you have everything to get started.
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### Install Node.js
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You may not need Node.js right now but you may need it for later. Install [node.js](https://nodejs.org/en/).
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After downloading double click and install
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We can check if node is installed on our local machine by opening our device terminal or command prompt.
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```sh
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asabeneh $ node -v
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v12.14.0
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```
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When making this tutorial I was using Node version 12.14.0, but now the recommended version of Node.js for download is v14.17.6, by the time you use this material you may have a higher Node.js version.
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### Browser
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There are many browsers out there. However, I strongly recommend Google Chrome.
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#### Installing Google Chrome
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Install [Google Chrome](https://www.google.com/chrome/) if you do not have one yet. We can write small JavaScript code on the browser console, but we do not use the browser console to develop applications.
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#### Opening Google Chrome Console
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You can open Google Chrome console either by clicking three dots at the top right corner of the browser, selecting _More tools -> Developer tools_ or using a keyboard shortcut. I prefer using shortcuts.
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To open the Chrome console using a keyboard shortcut.
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```sh
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Mac
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Command+Option+J
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Windows/Linux:
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Ctl+Shift+J
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```
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After you open the Google Chrome console, try to explore the marked buttons. We will spend most of the time on the Console. The Console is the place where your JavaScript code goes. The Google Console V8 engine changes your JavaScript code to machine code.
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Let us write a JavaScript code on the Google Chrome console:
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#### Writing Code on Browser Console
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We can write any JavaScript code on the Google console or any browser console. However, for this challenge, we only focus on Google Chrome console. Open the console using:
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```sh
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Mac
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Command+Option+I
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Windows:
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Ctl+Shift+I
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```
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##### Console.log
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To write our first JavaScript code, we used a built-in function **console.log()**. We passed an argument as input data, and the function displays the output. We passed `'Hello, World'` as input data or argument in the console.log() function.
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```js
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console.log('Hello, World!')
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```
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##### Console.log with Multiple Arguments
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The **`console.log()`** function can take multiple parameters separated by commas. The syntax looks like as follows:**`console.log(param1, param2, param3)`**
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```js
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console.log('Hello', 'World', '!')
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console.log('HAPPY', 'NEW', 'YEAR', 2020)
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console.log('Welcome', 'to', 30, 'Days', 'Of', 'JavaScript')
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```
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As you can see from the snippet code above, _`console.log()`_ can take multiple arguments.
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Congratulations! You wrote your first JavaScript code using _`console.log()`_.
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##### Comments
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We can add comments to our code. Comments are very important to make code more readable and to leave remarks in our code. JavaScript does not execute the comment part of our code. In JavaScript, any text line starting with // in JavaScript is a comment, and anything enclosed like this `//` is also a comment.
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**Example: Single Line Comment**
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```js
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// This is the first comment
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// This is the second comment
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// I am a single line comment
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```
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**Example: Multiline Comment**
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```js
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/*
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This is a multiline comment
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Multiline comments can take multiple lines
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JavaScript is the language of the web
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*/
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```
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##### Syntax
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Programming languages are similar to human languages. English or many other language uses words, phrases, sentences, compound sentences and other more to convey a meaningful message. The English meaning of syntax is _the arrangement of words and phrases to create well-formed sentences in a language_. The technical definition of syntax is the structure of statements in a computer language. Programming languages have syntax. JavaScript is a programming language and like other programming languages it has its own syntax. If we do not write a syntax that JavaScript understands, it will raise different types of errors. We will explore different kinds of JavaScript errors later. For now, let us see syntax errors.
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I made a deliberate mistake. As a result, the console raises syntax errors. Actually, the syntax is very informative. It informs what type of mistake was made. By reading the error feedback guideline, we can correct the syntax and fix the problem. The process of identifying and removing errors from a program is called debugging. Let us fix the errors:
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```js
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console.log('Hello, World!')
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console.log('Hello, World!')
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```
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So far, we saw how to display text using the _`console.log()`_. If we are printing text or string using _`console.log()`_, the text has to be inside the single quotes, double quotes, or a backtick.
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**Example:**
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```js
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console.log('Hello, World!')
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console.log("Hello, World!")
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console.log(`Hello, World!`)
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```
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#### Arithmetics
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Now, let us practice more writing JavaScript codes using _`console.log()`_ on Google Chrome console for number data types.
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In addition to the text, we can also do mathematical calculations using JavaScript. Let us do the following simple calculations.
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It is possible to write JavaScript code on Google Chrome console can directly without the **_`console.log()`_** function. However, it is included in this introduction because most of this challenge would be taking place in a text editor where the usage of the function would be mandatory. You can play around directly with instructions on the console.
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```js
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console.log(2 + 3) // Addition
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console.log(3 - 2) // Subtraction
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console.log(2 * 3) // Multiplication
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console.log(3 / 2) // Division
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console.log(3 % 2) // Modulus - finding remainder
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console.log(3 ** 2) // Exponentiation 3 ** 2 == 3 * 3
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```
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### Code Editor
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We can write our codes on the browser console, but it won't be for bigger projects. In a real working environment, developers use different code editors to write their codes. In this 30 days of JavaScript challenge, we will be using Visual Studio Code.
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#### Installing Visual Studio Code
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Visual Studio Code is a very popular open-source text editor. I would recommend to [download Visual Studio Code](https://code.visualstudio.com/), but if you are in favor of other editors, feel free to follow with what you have.
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|
||||
If you installed Visual Studio Code, let us start using it.
|
||||
|
||||
#### How to Use Visual Studio Code
|
||||
|
||||
Open the Visual Studio Code by double-clicking its icon. When you open it, you will get this kind of interface. Try to interact with the labeled icons.
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
## Adding JavaScript to a Web Page
|
||||
|
||||
JavaScript can be added to a web page in three different ways:
|
||||
|
||||
- **_Inline script_**
|
||||
- **_Internal script_**
|
||||
- **_External script_**
|
||||
- **_Multiple External scripts_**
|
||||
|
||||
The following sections show different ways of adding JavaScript code to your web page.
|
||||
|
||||
### Inline Script
|
||||
|
||||
Create a project folder on your desktop or in any location, name it 30DaysOfJS and create an **_`index.html`_** file in the project folder. Then paste the following code and open it in a browser, for example [Chrome](https://www.google.com/chrome/).
|
||||
|
||||
```html
|
||||
<!DOCTYPE html>
|
||||
<html lang="en">
|
||||
<head>
|
||||
<title>30DaysOfScript:Inline Script</title>
|
||||
</head>
|
||||
<body>
|
||||
<button onclick="alert('Welcome to 30DaysOfJavaScript!')">Click Me</button>
|
||||
</body>
|
||||
</html>
|
||||
```
|
||||
|
||||
Now, you just wrote your first inline script. We can create a pop up alert message using the _`alert()`_ built-in function.
|
||||
|
||||
### Internal Script
|
||||
|
||||
The internal script can be written in the _`head`_ or the _`body`_, but it is preferred to put it on the body of the HTML document.
|
||||
First, let us write on the head part of the page.
|
||||
|
||||
```html
|
||||
<!DOCTYPE html>
|
||||
<html lang="en">
|
||||
<head>
|
||||
<title>30DaysOfScript:Internal Script</title>
|
||||
<script>
|
||||
console.log('Welcome to 30DaysOfJavaScript')
|
||||
</script>
|
||||
</head>
|
||||
<body></body>
|
||||
</html>
|
||||
```
|
||||
|
||||
This is how we write an internal script most of the time. Writing the JavaScript code in the body section is the most preferred option. Open the browser console to see the output from the `console.log()`.
|
||||
|
||||
```html
|
||||
<!DOCTYPE html>
|
||||
<html lang="en">
|
||||
<head>
|
||||
<title>30DaysOfScript:Internal Script</title>
|
||||
</head>
|
||||
<body>
|
||||
<button onclick="alert('Welcome to 30DaysOfJavaScript!');">Click Me</button>
|
||||
<script>
|
||||
console.log('Welcome to 30DaysOfJavaScript')
|
||||
</script>
|
||||
</body>
|
||||
</html>
|
||||
```
|
||||
|
||||
Open the browser console to see the output from the `console.log()`.
|
||||
|
||||
|
||||
|
||||
### External Script
|
||||
|
||||
Similar to the internal script, the external script link can be on the header or body, but it is preferred to put it in the body.
|
||||
First, we should create an external JavaScript file with .js extension. All files ending with .js extension are JavaScript files. Create a file named introduction.js inside your project directory and write the following code and link this .js file at the bottom of the body.
|
||||
|
||||
```js
|
||||
console.log('Welcome to 30DaysOfJavaScript')
|
||||
```
|
||||
|
||||
External scripts in the _head_:
|
||||
|
||||
```html
|
||||
<!DOCTYPE html>
|
||||
<html lang="en">
|
||||
<head>
|
||||
<title>30DaysOfJavaScript:External script</title>
|
||||
<script src="introduction.js"></script>
|
||||
</head>
|
||||
<body></body>
|
||||
</html>
|
||||
```
|
||||
|
||||
External scripts in the _body_:
|
||||
|
||||
```html
|
||||
<!DOCTYPE html>
|
||||
<html lang="en">
|
||||
<head>
|
||||
<title>30DaysOfJavaScript:External script</title>
|
||||
</head>
|
||||
<body>
|
||||
<!-- JavaScript external link could be in the header or in the body -->
|
||||
<!-- Before the closing tag of the body is the recommended place to put the external JavaScript script -->
|
||||
<script src="introduction.js"></script>
|
||||
</body>
|
||||
</html>
|
||||
```
|
||||
|
||||
Open the browser console to see the output of the `console.log()`.
|
||||
|
||||
### Multiple External Scripts
|
||||
|
||||
We can also link multiple external JavaScript files to a web page.
|
||||
Create a `helloworld.js` file inside the 30DaysOfJS folder and write the following code.
|
||||
|
||||
```js
|
||||
console.log('Hello, World!')
|
||||
```
|
||||
|
||||
```html
|
||||
<!DOCTYPE html>
|
||||
<html lang="en">
|
||||
<head>
|
||||
<title>Multiple External Scripts</title>
|
||||
</head>
|
||||
<body>
|
||||
<script src="./helloworld.js"></script>
|
||||
<script src="./introduction.js"></script>
|
||||
</body>
|
||||
</html>
|
||||
```
|
||||
|
||||
_Your main.js file should be below all other scripts_. It is very important to remember this.
|
||||
|
||||
|
||||
|
||||
## Introduction to Data types
|
||||
|
||||
In JavaScript and also other programming languages, there are different types of data types. The following are JavaScript primitive data types: _String, Number, Boolean, undefined, Null_, and _Symbol_.
|
||||
|
||||
### Numbers
|
||||
|
||||
- Integers: Integer (negative, zero and positive) numbers
|
||||
Example:
|
||||
... -3, -2, -1, 0, 1, 2, 3 ...
|
||||
- Float-point numbers: Decimal number
|
||||
Example
|
||||
... -3.5, -2.25, -1.0, 0.0, 1.1, 2.2, 3.5 ...
|
||||
|
||||
### Strings
|
||||
|
||||
A collection of one or more characters between two single quotes, double quotes, or backticks.
|
||||
|
||||
**Example:**
|
||||
|
||||
```js
|
||||
'a'
|
||||
'Asabeneh'
|
||||
"Asabeneh"
|
||||
'Finland'
|
||||
'JavaScript is a beautiful programming language'
|
||||
'I love teaching'
|
||||
'I hope you are enjoying the first day'
|
||||
`We can also create a string using a backtick`
|
||||
'A string could be just as small as one character or as big as many pages'
|
||||
'Any data type under a single quote, double quote or backtick is a string'
|
||||
```
|
||||
|
||||
### Booleans
|
||||
|
||||
A boolean value is either True or False. Any comparisons returns a boolean value, which is either true or false.
|
||||
|
||||
A boolean data type is either a true or false value.
|
||||
|
||||
**Example:**
|
||||
|
||||
```js
|
||||
true // if the light is on, the value is true
|
||||
false // if the light is off, the value is false
|
||||
```
|
||||
|
||||
### Undefined
|
||||
|
||||
In JavaScript, if we don't assign a value to a variable, the value is undefined. In addition to that, if a function is not returning anything, it returns undefined.
|
||||
|
||||
```js
|
||||
let firstName
|
||||
console.log(firstName) // undefined, because it is not assigned to a value yet
|
||||
```
|
||||
|
||||
### Null
|
||||
|
||||
Null in JavaScript means an empty value.
|
||||
|
||||
```js
|
||||
let emptyValue = null
|
||||
```
|
||||
|
||||
## Checking Data Types
|
||||
|
||||
To check the data type of a certain variable, we use the **typeof** operator. See the following example.
|
||||
|
||||
```js
|
||||
console.log(typeof 'Asabeneh') // string
|
||||
console.log(typeof 5) // number
|
||||
console.log(typeof true) // boolean
|
||||
console.log(typeof null) // object type
|
||||
console.log(typeof undefined) // undefined
|
||||
```
|
||||
|
||||
## Comments Again
|
||||
|
||||
Remember that commenting in JavaScript is similar to other programming languages. Comments are important in making your code more readable.
|
||||
There are two ways of commenting:
|
||||
|
||||
- _Single line commenting_
|
||||
- _Multiline commenting_
|
||||
|
||||
```js
|
||||
// commenting the code itself with a single comment
|
||||
// let firstName = 'Asabeneh'; single line comment
|
||||
// let lastName = 'Yetayeh'; single line comment
|
||||
```
|
||||
|
||||
Multiline commenting:
|
||||
|
||||
```js
|
||||
/*
|
||||
let location = 'Helsinki';
|
||||
let age = 100;
|
||||
let isMarried = true;
|
||||
This is a Multiple line comment
|
||||
*/
|
||||
```
|
||||
|
||||
## Variables
|
||||
|
||||
Variables are _containers_ of data. Variables are used to _store_ data in a memory location. When a variable is declared, a memory location is reserved. When a variable is assigned to a value (data), the memory space will be filled with that data. To declare a variable, we use _var_, _let_, or _const_ keywords.
|
||||
|
||||
For a variable that changes at a different time, we use _let_. If the data does not change at all, we use _const_. For example, PI, country name, gravity do not change, and we can use _const_. We will not use var in this challenge and I don't recommend you to use it. It is error prone way of declaring variable it has lots of leak. We will talk more about var, let, and const in detail in other sections (scope). For now, the above explanation is enough.
|
||||
|
||||
A valid JavaScript variable name must follow the following rules:
|
||||
|
||||
- A JavaScript variable name should not begin with a number.
|
||||
- A JavaScript variable name does not allow special characters except dollar sign and underscore.
|
||||
- A JavaScript variable name follows a camelCase convention.
|
||||
- A JavaScript variable name should not have space between words.
|
||||
|
||||
The following are examples of valid JavaScript variables.
|
||||
|
||||
```js
|
||||
firstName
|
||||
lastName
|
||||
country
|
||||
city
|
||||
capitalCity
|
||||
age
|
||||
isMarried
|
||||
|
||||
first_name
|
||||
last_name
|
||||
is_married
|
||||
capital_city
|
||||
|
||||
num1
|
||||
num_1
|
||||
_num_1
|
||||
$num1
|
||||
year2020
|
||||
year_2020
|
||||
```
|
||||
|
||||
The first and second variables on the list follows the camelCase convention of declaring in JavaScript. In this material, we will use camelCase variables(camelWithOneHump). We use CamelCase(CamelWithTwoHump) to declare classes, we will discuss about classes and objects in other section.
|
||||
|
||||
Example of invalid variables:
|
||||
|
||||
```js
|
||||
first-name
|
||||
1_num
|
||||
num_#_1
|
||||
```
|
||||
|
||||
Let us declare variables with different data types. To declare a variable, we need to use _let_ or _const_ keyword before the variable name. Following the variable name, we write an equal sign (assignment operator), and a value(assigned data).
|
||||
|
||||
```js
|
||||
// Syntax
|
||||
let nameOfVariable = value
|
||||
```
|
||||
|
||||
The nameOfVriable is the name that stores different data of value. See below for detail examples.
|
||||
|
||||
**Examples of declared variables**
|
||||
|
||||
```js
|
||||
// Declaring different variables of different data types
|
||||
let firstName = 'Asabeneh' // first name of a person
|
||||
let lastName = 'Yetayeh' // last name of a person
|
||||
let country = 'Finland' // country
|
||||
let city = 'Helsinki' // capital city
|
||||
let age = 100 // age in years
|
||||
let isMarried = true
|
||||
|
||||
console.log(firstName, lastName, country, city, age, isMarried)
|
||||
```
|
||||
|
||||
```sh
|
||||
Asabeneh Yetayeh Finland Helsinki 100 true
|
||||
```
|
||||
|
||||
```js
|
||||
// Declaring variables with number values
|
||||
let age = 100 // age in years
|
||||
const gravity = 9.81 // earth gravity in m/s2
|
||||
const boilingPoint = 100 // water boiling point, temperature in °C
|
||||
const PI = 3.14 // geometrical constant
|
||||
console.log(gravity, boilingPoint, PI)
|
||||
```
|
||||
|
||||
```sh
|
||||
9.81 100 3.14
|
||||
```
|
||||
|
||||
```js
|
||||
// Variables can also be declaring in one line separated by comma, however I recommend to use a seperate line to make code more readble
|
||||
let name = 'Asabeneh', job = 'teacher', live = 'Finland'
|
||||
console.log(name, job, live)
|
||||
```
|
||||
|
||||
```sh
|
||||
Asabeneh teacher Finland
|
||||
```
|
||||
|
||||
When you run _index.html_ file in the 01-Day folder you should get this:
|
||||
|
||||
|
||||
|
||||
🌕 You are amazing! You have just completed day 1 challenge and you are on your way to greatness. Now do some exercises for your brain and muscle.
|
||||
|
||||
# 💻 Day 1: Exercises
|
||||
|
||||
1. Write a single line comment which says, _comments can make code readable_
|
||||
2. Write another single comment which says, _Welcome to 30DaysOfJavaScript_
|
||||
3. Write a multiline comment which says, _comments can make code readable, easy to reuse_
|
||||
_and informative_
|
||||
|
||||
4. Create a variable.js file and declare variables and assign string, boolean, undefined and null data types
|
||||
5. Create datatypes.js file and use the JavaScript **_typeof_** operator to check different data types. Check the data type of each variable
|
||||
6. Declare four variables without assigning values
|
||||
7. Declare four variables with assigned values
|
||||
8. Declare variables to store your first name, last name, marital status, country and age in multiple lines
|
||||
9. Declare variables to store your first name, last name, marital status, country and age in a single line
|
||||
10. Declare two variables _myAge_ and _yourAge_ and assign them initial values and log to the browser console.
|
||||
|
||||
```sh
|
||||
I am 25 years old.
|
||||
You are 30 years old.
|
||||
```
|
||||
|
||||
🎉 CONGRATULATIONS ! 🎉
|
||||
|
||||
[Day 2 >>](./02_Day_Data_types/02_day_data_types.md)
|
||||
Loading…
Reference in new issue