30 Days Of React: Getting Started React

Twitter Follow Author: Asabeneh Yetayeh
October, 2020
[<< Day 1](../readMe.md) | [Day 3 >>](../03_Day_Booleans_operators_date/03_booleans_operators_date.md) ![30 Days of React banner](../images/30_days_of_react_banner_day_2.jpg) - [Getting Started React](#getting-started-react) - [1. What is React?](#1-what-is-react) - [2. Why React?](#2-why-react) - [React vs Vue popularity in October 2020](#react-vs-vue-popularity-in-october-2020) - [React vs Vue popularity in February 2020](#react-vs-vue-popularity-in-february-2020) - [3. JSX](#3-jsx) - [JSX Element](#jsx-element) - [Commenting JSX element](#commenting-jsx-element) - [Rendering JSX Element](#rendering-jsx-element) - [Style and className in JSX](#style-and-classname-in-jsx) - [Exercises](#exercises) - [Exercises: What is React?](#exercises-what-is-react) - [Exercises: Why React?](#exercises-why-react) - [Exercises: JSX](#exercises-jsx) - [Exercises: JSX Elements](#exercises-jsx-elements) - [Exercises: Inline Style](#exercises-inline-style) - [Exercises: Internal Styles](#exercises-internal-styles) ## Getting Started React Prerequisite to get started with React. You should have a good understanding of the following technologies: - HTML - CSS - JavaScript If you have the above skills you will enjoy doing React. React for Everyone contains anything you need to know about react. In every section, it has some exercises and mini-projects and it is recommended to work on them. This 30 Days Of React challenge will help you learn the latest version of React and the old version step by step. The topics are broken down into 30 days, where each day contains several topics with easy-to-understand explanations, real-world examples and many hands on exercises. This challenge is designed for beginners and professionals who want to build a web application using React and JavaScript. ### 1. What is React? React is a JavaScript library for building a reusable user interface(UI). It was initially released on May 29, 2013. The current version is 16.13.1 and somehow it is stable. React was created by Facebook. React makes creating UI components very easy.The official React documentation can be found [here](https://reactjs.org/docs/getting-started.html). When we work with React we do not interact directly with the DOM. React has its own way to handle the DOM(Document Object Model) manipulation. React uses its virtual DOM to make a new change and it updates only the element that needs change. Do not directly interact with DOM when you build a React Application and leave the DOM manipulation job for the React virtual DOM. In this challenge, we will develop 10-15 web applications using React. A web application or a website is made up of buttons, links, forms with different input fields, header, footer, sections, articles, texts, images, audios, videos and boxes with different shapes. We use react to make a reusable UI component of a website. To summarize: - React was released in May 2013 - React was created by Facebook - React is a JavaScript library for building user interfaces - React is used to build single page applications- An application which has only one HTML page. - React allows us to create reusable UI components - React latest release is 16.13.1 - [React versions](https://reactjs.org/versions/) - React official documentation can be found [her](https://reactjs.org/docs/getting-started.html) ### 2. Why React? React is one of the most popular JavaScript library. Many developers and companies have been using it for the last couple of years. Its popularity has been growing fast and it has a huge community. How do we measure popularity? One measure of popularity could be GitHub repository stars, watchers and forks. Let us compare the popularity of [React](https://github.com/facebook/react) and [Vue](https://github.com/vuejs/vue). As of today, the popularity between the two most popular JavaScript looks like as shown on the diagram. From the diagram, you can speculate the most popular JavaScript library. You may look at the number of watchers, stars and forks for both React and Vue. These alone will not be a very good measure of popularity but still it tells a little bit about the popularity of the two technologies. If I have to recommend another JavaScript library next to React would Vue.js. #### React vs Vue popularity in October 2020 React Official GitHub Repository ![React Popularity October 2020](../images/react_repo_1_oct_2020.png) Vue Official GitHub Repository ![Vue Popularity October 2020](../images/vue_repo_1_oct_2020.png) #### React vs Vue popularity in February 2020 React Official GitHub Repository ![React Popularity February 2020](../images/react_popularity.png) Vue Official GitHub Repository ![Vue Popularity February 2020](../images/vue_popularity.png) Why we choose to use react ? We use react because of the following reasons: - fast - modular - scalable - flexible - big community and popular - open source - High job opportunity ### 3. JSX JSX stands for JavaScript XML. JSX allows us to write HTML elements with JavaScript code. An HTML element has an opening and closing tag, content, and attribute in the opening tag. However, some HTML tag may not have a content and a closing tag, they are self closing elements. To create HTML elements in React we do not use the _createElement()_ instead we just use JSX elements. Therefore, JSX makes it easier to write and add HTML elements in React. JSX will be converted to JavaScript on browser using transpiler which [babel.js](https://babeljs.io/). Babel is a library which transpile JSX to pure JavaScript and latest JavaScript to older version. See the JSX code below. ```js // JSX syntax // we don't need to use quotes with use JSX const jsxElement =

I am a JSX element

const welcome =

Welcome to 30 Days of React Challenge

const data = Oct 2, 2020 ``` The above strange looking code seems a JavaScrip but it is not JavaScript and it seems an HTML but not completely an HTML element. It is a mix of JavaScript and an HTML element. JSX can allow us to use HTML in JavaScript. The HTML element in the above JSX is _h1_ and _small_. #### JSX Element As you have seen in the above example, JSX has a JavaScript and HTML like syntax. JSX element could be a single HTML element or many HTML elements wrapped in a parent HTML element. This JSX element has only on HTML element which is _h1_. ```js const jsxElement = I am a JSX element // JS with HTML ``` Let's make more JSX elements by declaring a new variable name title and content inside h1. ```js const title =

Getting Started React

``` Let us add a subtitle and other contents to the above JSX element by adding additional HTML elements. Every HTML element should be wrapped by an outer HTML element to create a valid JSX element. The name title variable also should be changed to header because our JSX element is containing almost all the header of the application. ```js const header = (

Welcome to 30 Days Of React

Getting Started React

JavaScript Library

) ``` Let us keep adding more elements. Additional HTML element to display the author name and year. ```js const header = (

Welcome to 30 Days Of React

Getting Started React

JavaScript Library

Asabeneh Yetayeh

Oct 2, 2020
) ``` As you can see the _header_ element is a parent element for all the inner HTML elements and JSX must be wrapped by an outer parent element. Without the _header_ HTML element or other parent HTML element the above JSX is invalid. #### Commenting JSX element We comment codes for different reasons and it is also go to know how to comment out JSX element in React. ```js { /*

Welcome to 30 Days Of React

Getting Started React

JavaScript Library

Asabeneh Yetayeh

Oct 2, 2020
*/ } ``` #### Rendering JSX Element To render a JSX element to HTML document, we should first create an index HTML. The index.html is the only HTML file you will have in any React Application. That is why we call that every React Application is a single page application. Let us create an index.html file. ```html 30 Days Of React Challenge
``` As you can see from the above index.html, we have one div with a class root and script. The root _div_ is the get way to connect all react component to the index.html. In the script tag, we will write our JavaScript but the script _type_ will be _babel_. Babel will _transpile_ the react JSX to pure JavaScript on the browser. Let us add babel to the script. Inside the babel, we can write any pure JavaScript, JSX and in general any react code. ```html 30 Days Of React Challenge
``` The babel library is linked to our document and now we can make use of it. The next step is importing _React_ and _ReactDOM_ using CDN or link. In order to link React and ReactDOM we attach both packages CDN to the body of index.html. To test if React is linked to the index.html try to check by doing console.log(React). Open the browser console and you should get an object. If you see an object containing React methods then you managed to link your project with React CND and you are ready to use React. ```html 30 Days Of React Challenge
``` Now the index.html has everything we need to write React code. Let us get the root element using document.querySelect('.root') and assign it to a variable name rootElement. The is the only place we directly interact with DOM. Now, you knew JSX and JSX element. Let us render the JSX element on the browser, in order to do so we need the React and ReactDOM library. In addition to the React and ReactDOM we need babel to transpile the JSX to JavaScript code. The ReactDOM package has a method render. The render method takes two arguments:a JSX element or a component and the root document. See the code below. [Live on code pen](https://codepen.io/Asabeneh/full/JjdbjqK). ```html 30 Days Of React Challenge
``` ![Rendering JSX](../images/rendering_jsx.png) Let us render more content. To render more content, the JSX element should have more HTML elements. For instance, we can create a header of a website and header may have a title, subtitle, author or date etc. Remember, we can render only one on JSX element at a time. [Live on code pen](https://codepen.io/Asabeneh/full/QWbGWeY). ```html 30 Days Of React Challenge
``` ![Rendering more content](../images/rendering_more_jsx_content_.png) We have created a JSX element for the header of the website. How about the main and the footer for the website? Similar to the header, let us create a JSX element for the main and the footer. JSX element for the main part of the website. ```js // JSX element const main = (

Prerequisite to get started react.js:

) ``` JSX element for the footer part of the website. ```js // JSX element const footer = ( ) ``` Now, we have three JSX elements:the header, main and footer. The best way to render all the three JSX elements is by wrapping them all in a parent JSX element or putting them in an array. To include JSX element inside another JSX element we use the curly bracket, {} and call the name of the JSX inside the curly bracket. ```js // JSX element for the header part of the website const header = (

Welcome to 30 Days Of React

Getting Started React

JavaScript Library

Asabeneh Yetayeh

Oct 2, 2020
) // JSX element for the main part of the website const main = (

Prerequisite to get started react.js:

) // JSX element for the footer part of the website const footer = ( ) // JSX element which contain all, it is a container or parent const app = (
{header} {main} {footer}
) ``` Now, let us put everything together and render it to the browser. [Live on code pen](https://codepen.io/Asabeneh/full/MWwbYWg). ```html 30 Days Of React Challenge
``` ![Rendering Multiple JSX Elements](../images/rendering_multiple_jsx_elements.png) Let us apply some style to our JSX elements and see the result. ![Styling JSX Element](../images/styling_jsx_element.png). Now, lets us apply style the header part only [Live on code pen](https://codepen.io/Asabeneh/full/ZEGBYBG). #### Style and className in JSX So far, we did not apply any style in the JSX elements. Now, let us add style to our JSX elements. Inline style became very popular after the emergence of react. Let us add border to the header JSX element. To add style to a JSX element we use inline style or className. We inject the style object using {}. Every CSS properties become a key and every CSS properties value become value for the the object. For instance, in the example below, border is a key and '2px solid orange' is a value, color is a key and 'black' is a value, fontSize is a key and '18px' is a value. All two word CSS properties will change to camelCase when we use them as key in the CSS object in react or JavaScript.[Live on code pen](https://codepen.io/Asabeneh/full/ZEGBYbY). ```js const header = (

Welcome to 30 Days Of React

Getting Started React

JavaScript Library

Asabeneh Yetayeh

Oct 2, 2020
) // or we can write it const style = { border: '2px solid orange', color: 'black', fontSize: '18px' } const header = (

Welcome to 30 Days Of React

Getting Started React

JavaScript Library

Asabeneh Yetayeh

Oct 2, 2020
) ``` It is good practice to open the browser console while you are developing your application to know if everything goes well. Let us keep styling all the JSX elements we have created: the header, main and footer. We can also use regular internal styling to style our application. Using regular style, to target an HTML element we use tag name, id, class, an attribute and other methods. It is very common in the react developer community people use quite a lot classes instead of id. In this material, I will use only class instead of id. In JSX element we write className instead of class because class is a reserved word in JavaScript. Similar to className, htmlFor instead of for in label tag. See the example below. ```js const title =

Getting Started React

const inputField = (
) ``` The id used in the input element is not for styling purpose instead to refer the label to the input field. If class is used instead of className or for instead of htmlFor you will see such kind of warning. ![Class Name warning](../images/className_warning.png) Now, you know how to use the inline style and how to use className and let us style all the JSX elements. ```html 30 Days Of React Challenge
``` ![Styling all jsx elements](../images/styling_all_jsx_elements.png) Instead of style object using regular styling method is more easier than the above. Now, let us use internal style to style all the JSX. It is also possible to use external style method.[Live on code pen](https://codepen.io/Asabeneh/full/QWbGwge) ```html React For Everyone
``` ![Internal Style](../images/internal_style.png) 🌕 You are awesome. You have just completed day 2 challenges and you are two steps ahead on your way to greatness. Now do some exercises for your brain and for your muscle. ### Exercises #### Exercises: What is React? 1. What is React? 2. What is a library ? 3. What is single page application ? 4. What is component ? 5. What is the latest version of react ? 6. What is DOM ? 7. What is React Virtual DOM 8. What does a web application or a website(composed of) may have? #### Exercises: Why React? 1. Why you chose to use react? 2. What measures do you use to know popularity ? 3. What is more popular, react or Vue ? #### Exercises: JSX 1. What is an HTML element ? 2. Write is a self closing HTML element ? 3. What is HTML attribute, write some HTML attributes ? 4. What is JSX ? 5. What is babel ? 6. What is a transpiler? #### Exercises: JSX Elements 1. What is JSX element 2. Write your name in JSX element and store it in a name variable 3. Write a JSX element which displays your full name, country, title, gender, email, phone number. Use h1 for the name and p for the rest of the information and store it in a user variable. 4. Write a footer JSX element #### Exercises: Inline Style 1. Create a style object for the main JSX 2. Create a style object for the footer and app JSX 3. Add more styles to the JSX elements #### Exercises: Internal Styles 1. Apply different styles to your JSX elements 🎉 CONGRATULATIONS ! 🎉 [<< Day 1](../readMe.md) | [Day 3 >>](../03_Day_Setting_Up/03_day_setting_up.md)