In this book, you've learned how to apply best practices when writing a React application. In the first few chapters, we revisited the basic concepts to build a solid understanding, and then we took a leap into more advanced techniques in the following chapters.

You should now be able to build reusable components, make components communicate with each other, and optimize an application tree to get the best performance. However, developers make mistakes, and this chapter is all about the common anti-patterns we should avoid when using React.

Looking at common errors will help you to avoid them and will aid your understanding of how React works and how to build applications in the React way. For each problem, we will see an example that shows how to reproduce and solve it.

In this chapter, we will cover the following topics:

• Initializing the state using properties
• Mutating the state 
• Using indexes as a key
• Spreading properties on DOM elements