This chapter contains recipes related to how to create components in React. We are going to learn how to create React components (class components, pure components, and functional components) and organize our project structure. We'll also learn how to use React local state, implement all the React lifecycle methods, and finally, we'll see how to prevent XSS vulnerabilities.

The component is the essential part of React. With React you can build interactive and reusable components. In this recipe, you will create your first React component.

First, we need to create our React application using create-react-app. Once that is done, you can proceed to create your first React component.

Before you install create-react-app, remember that you need to download and install Node from www.nodejs.org. You can install it for Mac, Linux, and Windows.

Install create-react-app globally by typing this command in your Terminal:

  npm install -g create-react-app

Or you can use a shortcut:

  npm i -g create-react-app

In this recipe, we will learn how to structure our project in a better way.

We can create React components with the default structure that create-react-app provides, but in this recipe, I'll show you a better way to organize the project so that we are ready when for when the application grows.

1. We need to create a new React app (check the last recipe if you haven't created a React app yet)

2. Currently, our React application directory tree looks like this:

3. We need to create src/components and src/shared directories
4. After this, we need to create the src/components/Home directory for our component and move Home.js into this folder
5. The App.js file stays...

In the last recipe, we learned how to create a class component. Now let's add some CSS to our Home component.

In React, one of the best practices is to have the style file in the same directory as the component. If you have worked with PHP, Node, or any other server language, you probably write your styles in a style.css file, and you include it using a link tag in your template. React uses Webpack, which is the most popular module bundler at the moment. With Webpack, we can configure the way that we want to handle our styles (using CSS directly or by using a CSS preprocessor such as Sass, Stylus, or Less CSS), and with Webpack we can implement CSS modules. This is a powerful way to avoid the three main issues of CSS:

• No more conflicts (unintentional CSS...

So far, you are getting familiar with React components, but there is more to it than rendering static HTML. Like any application, we need to be able to send information (via props) to different elements. In this recipe, we are going to create new components: Header, Content, and Footer (we will group these components into a folder called layout), and we will send some props (as attributes and as children) and validate them with PropTypes.

Taking the same of the React application we created before, let's create first our Header component. 

1. At this point, our current header is placed on...

The local state is a fundamental feature of React for creating dynamic components. Local state is only available on class components, and each component manages its state. You can define the initial value of the state on the component's constructor, and when you update the value of the state, the component will be re-render itself.

Local state is helpful with toggles, for handling forms, and is used to manage information within the same component. It is not recommended to use local state if we need to share data between different components. In that scenario, we need to implement Redux state, which we will cover in Chapter 5, Mastering Redux.

So far, we have only learned how to create class components in React. These components are useful when you need to handle local state, but in some cases, we will need to render static markup. For static components, we need to use functional components, also known as stateless components. This will improve the performance of our application.

In the Passing props to a component and validating them with PropTypes recipe, we created some layout components (Header, Content, and Footer). These components, as you may imagine, are frequently not dynamic (unless you want to have a toggle menu or some user information in the header), so in this case, we can convert them into functional components.

React provides methods to handle the data during the lifecycle of a component. This is very useful when we need to update our application at particular times.

In this section, we are going to explain each example independently.

In this recipe, you will learn about the lifecycle methods in React. We will see how the information flows through the methods since the component is pre-mounted, mounted, and unmounted. The Todo list that we will develop...

Many people get confused by the difference between a Functional Component and a Pure Component. Most of them think they are the same, but this is not true. When we use a Pure Component, we need to import PureComponent from React:

    import React, { PureComponent } from 'react';

If your React component's render method is "pure" (that means it renders the same result, given the same props and state), you can use this function to improve the performance of your application. A Pure Component performs a shallow comparison for the props and nextProps objects as well as the state and nextState objects. Pure components do not include the shouldComponentUpdate(nextProps, nextState) method, and if we try to add it, we will get a warning from React.

In this recipe, we will create a basic example to understand how Pure Components...

In this recipe, we are going to learn about cross-site scripting (XSS) vulnerabilities in React. XSS attacks are widespread in web applications, and some developers are still not aware of this. XSS attacks are malicious scripts that are injected into the DOM of unprotected web applications. The risks can vary with each application. It could just be an innocent alert script injection or, worse, someone can get access to your cookies and steal your private credentials (passwords), for example.

Let's create an XSS component to start playing around a little bit with some XSS attacks. We are going to have a response variable that is simulating a response from a real server, and we will simulate that we are using Redux's initial state (we are going to see Redux in ...