React js book free download

For example this is a common statement you will find in JSX. What do we mean by state? The state is the set of data that is managed by the component. Think about a form, for example. Each individual input element of the form is responsible for managing its state: what is written inside it. We manage state using the useState utility provided by React.

It's technically a hook you don't need to know the details of hooks right now, but that's what it is. Calling useState , you will get back a new state variable, and a function that we can call to alter its value.

This is important. We can't just alter the value of a state variable directly. We must call its modifier function. Otherwise the React component will not update its UI to reflect the changes of the data. The syntax is a bit weird, right?

You can add as many useState calls as you want, to create as many state variables as you want:. Now that we have the prop, we can use it inside the component. For example we can print its value in the JSX:. Curly brackets here have various meanings.

In the case of the function argument, curly brackets are used as part of the object destructuring syntax. Then we use them to define the function code block, and finally in the JSX to print the JavaScript value. We can also send functions as props, so a child component can call a function in the parent component. A special prop is called children. That contains the value of anything that is passed between the opening and closing tags of the component, for example:.

In this case, inside WelcomeMessage we could access the value Here is some message by using the children prop:.

In a React application, data typically flows from a parent component to a child component, using props as we saw in the previous section:.

If you pass a function to the child component, you can however change the state of the parent component from a child component:.

Inside the Counter component we can now grab the setCount prop and call it to update the count state in the parent component, when something happens:.

You need to know that there are more advanced ways to manage data, which include the Context API and libraries like Redux. React provides an easy way to manage events fired from DOM events like clicks, form events, and more. When the click event is fired on the button, React calls the event handler function. The useEffect hook allows components to have access to the lifecycle events of a component.

When you call the hook, you pass it a function. We do this by adding a second parameter which is an array that contains a list of state variables to watch for. Similarly, you can tell React to only execute the side effect once at mount time , by passing an empty array:.

Mastering the topics explained in this article is a great step towards your goal of learning React. I want to give you some pointers now, because it's easy to get lost in the sea of tutorials and courses about React. Learn more theory about the Virtual DOM , writing declarative code , unidirectional data flow , immutability , composition.

Start building some simple React applications. For example build a simple counter or a interact with a public API. Learn how to test React applications. Learn an application framework built on top of React, like Gatsby or Next. Most of all, make sure you practice by building sample applications to apply everything you've learned. I publish programming tutorials every day on my website flaviocopes.

If this article was helpful, tweet it. Learn to code for free. Get started. Forum Donate. Flavio Copes. The goal of this handbook is to provide a starter guide to learning React. At the end of the book, you'll have a basic understanding of: What React is and why it's so popular How to install React React Components React State React Props Handling user events in React Lifecycle events in a React component These topics will be the base upon which you will build in other more advanced React tutorials.

What is React? React is a JavaScript library that aims to simplify the development of visual interfaces. React in itself has a very small API, and you basically need to understand 4 concepts to get started: Components JSX State Props We'll explore all of these in this book, and we'll leave the more advanced concepts to other tutorials.

You don't have to be a JavaScript expert, but I think you need a good overview of: Variables Arrow functions Work with objects and arrays using Rest and Spread Object and array destructuring Template literals Callbacks ES Modules If those concepts sound unfamiliar, I've provided you with some links to find out more about those subjects.

Why should you learn React? I highly recommend that any Web developer has at least a basic understanding of React. That's because of a few reasons. React is very popular. As a developer, it's quite likely that you're going to work on a React project in the future. There are books for almost everything. See credits at the end of this book whom contributed to the various chapters.

Images may be copyright of their respective owners unless otherwise specified. Book created for educational purposes and is not affiliated with React JS group s , company s nor Stack Overflow. All trademarks belong to their respective company owners. React JS Notes for Professionals book. Want to learn React? React Native is a framework for building cross-platform apps. Building with React Native is extremely efficient and highly addictive — but getting started can be a little tricky.

This free online book, React Native Express can be used as a companion to the official Facebook documentation for getting started.