Create React App

There is a very useful package called create-react-app which will automatically install all your required dependencies, and set up a directory for your react app automatically.

Using Create React App

1. Install Create React App globally npm install -g creat-react-app
2. From the command line type npx create-react-app app-name

This will create a directory for the front end of your app called app-name. Inside that there will be a package.json file with all the scripts you need to create a react app, run it locally, and build a production version of that site.

The directory (app-name in this example) is automatically set up as a git repository

Directory Structure

There are two main parts of the create-react-app directory

• the src folder
• the public folder

If you create a production build with npm run build you will additionally have a build folder. More on that when we talk about serving React projects next week!

Core Concept: the src folder

The src folder is where the meat of your React project lives

• Create a JS file for each component
• Import components where needed
• The App.js file lays out the whole page
• index.js draws the content to the page
• CSS for your project also goes in here

Core Concept: the public folder

The public folder is where your react component gets drawn to.

• Contains index.html
• Displays the front end of the app
• Keep images you want to display in here
• Don't tweak the HTML!

Lab: Create a React Component

Let's create our first React Component! If you haven't already installed create-react-app go ahead and do that now npm install -g create-react-app

• cd into your code folder
• create a React app named first-reapp
• Change your app so it displays an h1 with the text "Hello, React!"

Note: After you open VSCode it will ask if you want to use eslint from node modules. React has it's own eslint extension to properly highlight react components so use it.

Core Concept: Functional Components

By default create-react-app will set you up with a functional component.

Functional components are just functions that return JSX

But React still needs to be in scope for a functional component to work, even theough it's not explicitly used in the component

Core Concept: Class Based Components

Class based components are an older way of setting up React Components, and are more representative of the way react actually works.

They are slightly less readable, and as of React 16.8 are less common since Hooks allow functional components to have all the same functionality.

This transition from class based to functional components happened very quickly not too long ago so a lot of documentation still uses class based components.

The State Object

Every React component keeps track of its own state in an internal object named state. In a class based component you can access state through this.state. In a functional component you have to use Hooks to access state.

React likes to be in complete control of the page so it's important to only update the page through state, and never through direct DOM manipulation!

Never Directly Manipulate the DOM

This is very important, and bears repeating.

Never directly manipulate the DOM when using React. All changes should be made through the state of the component using this.setState if it's a class based component, or the useState hook if it's a functional component.

Direct manipulation of the DOM will confuse React, and cause bugs.

Lifecycle Methods

Class based components also have direct access to a component's lifecycle methods. These are methods which get called at certain points during the component's life.

The most common of these are:

• componentDidMount fires when the component is first loaded onto the page
• componentDidUpdate fires whenever props or state are updated
• componentWillUnmount fires right before the component is removed from the page

Lifecycle Diagram