Master React JS fundamentals interactively

Introduction to Learning React JS

React JS has rapidly grown in popularity and usage over the past few years to become one of the most widely used frameworks for building modern web applications. Created and open sourced by Facebook engineers Jordan Walke and Tom Occhino in 2013, React enables developers to build composable user interfaces by breaking them down into reusable, modular components.

With over 100k stars on GitHub and powering thousands of high-profile apps including Facebook, Instagram, Netflix, and Discord, learning React is an invaluable skill for any front-end developer and expands career opportunities. This interactive course aims to teach you React fundamentals from the ground up and provide practical experience through coding challenges and real-world projects.

By the end, you'll have a solid grasp of core concepts like JSX syntax, components, props, state, lifecycle methods, hooks, routing, and state management. You'll gain the ability to develop complex, reactive user interfaces with composable React components. The knowledge you gain will transfer directly to building mobile apps with React Native as well.

What is React JS?

React is an open-source JavaScript library created by Facebook for building fast and interactive user interfaces for web and mobile applications. Here are some of its key characteristics:

• It's a library for creating reactive and stateful user interfaces using components
• Components are reusable, encapsulated pieces of UI code and logic
• It uses a virtual DOM to efficiently update changes rather than directly manipulating the DOM
• This enables fast rendering and excellent performance at scale
• React follows a unidirectional data flow model and handles updates declaratively
• Bindings update reactively when underlying data changes

For example:

// Header.js

function Header() {
  return (
    <header>
      <h1>My Website</h1>
    </header>
  ); 
}

This Header component encapsulates the header markup and can be reused throughout the application.

Why Learn React JS?

There are many great reasons to learn React JS:

• React is incredibly popular with over 100,000 stars on GitHub
• It powers thousands of impressive apps like Facebook, Instagram, Netflix, Discord
• Knowledge of React is a highly sought after skill for frontend developer jobs
• React enables building complex, interactive UIs that were difficult with plain JavaScript
• The knowledge transfers well to React Native for mobile development
• There is a thriving ecosystem of libraries and tools like React Router, Redux, Create React App
• React encourages reusable, modular UI components and code

Core Concepts of React

React is built around several key concepts:

• Components - Reusable, encapsulated code modules that take in props and return JSX. Components define the UI building blocks.
• JSX - Allows mixing HTML with JavaScript code for templating UI. JSX gets compiled to JavaScript.
• Props - Inputs passed to a component like attributes. Allow passing data to components.
• State - Components can manage internal state data that determines rendering.
• Virtual DOM - A JavaScript representation of the actual DOM.
• Unidirectional Data Flow - Data in React apps flows in one direction down through the component hierarchy.
• Lifecycle Methods - Methods that run at certain points in a component's lifecycle like mounting, updating, and unmounting.
• State Management - Managing state with Hooks, Context API or external libraries like Redux.

What You'll Learn

By the end of this course, you should feel comfortable with:

• Fundamentals like JSX syntax, components, props, state, lifecycle methods
• Creating reusable UI components and applying best practices
• Hooks for state management in function components
• Debugging, testing React components with Jest
• Routing with React Router, state management with Context API or Redux
• Advanced patterns like higher-order components and render props
• Optimizations like code splitting, lazy loading, suspense
• Building and deploying React apps

With a strong grasp of these concepts, you'll be prepared to create feature-rich React applications from scratch. Let's start by setting up our React development environment.

Setting Up Your React Environment

Before diving into React code, you need to set up an effective React development environment. This includes choosing a starter project, an editor or IDE, installing Node.js and npm, and identifying helpful React libraries.

Creating a New React App

The easiest way to start a React project is using Create React App (CRA). It sets up a project with:

• Babel and webpack already configured
• Hot reloading development server
• Jest testing framework
• Production build scripts

The default CRA project gives you a solid folder structure with /src and /public folders. Ejecting lets you customize the configuration.

Choosing an IDE

Some popular options for writing React code include:

• VS Code - Free and hugely popular editor with great React support
• WebStorm - Robust IDE well-suited for JavaScript and React
• Atom - Hackable editor with many community React packages
• Sublime Text - Fast and lightweight with plugins for React development

Installing Node.js

You'll need Node.js installed to run JavaScript outside the browser and manage dependencies with npm. Consider version managers like nvm for switching Node versions easily.

Key things to know about npm and package.json:

• npm install adds dependencies to node_modules
• package.json stores project config, dependencies, scripts
• Semantic versioning is used for specifying dependency versions

Helpful React Libraries

Here are some useful libraries to consider for a React project:

• React Router - Declarative routing for React applications
• Redux - State management with centralized store and actions
• Axios - Promise based HTTP client for calling APIs
• Material UI - Popular React UI framework with many components
• Formik - Form validation and submission handling
• React i18next - Internationalization and translation

Equipped with this dev environment, you're ready to learn core React concepts.

Core React Concepts and JSX

Now that you have your dev environment setup, it's time to learn foundational React concepts. This includes an introduction to components, JSX, rendering UI, and handling events and state.

React Components

The building blocks of React apps are reusable, modular components that encapsulate UI logic and markup:

• Components can be classes or functions - often called function components
• Components receive data through props and maintain internal state
• Best practice is splitting UI into a component hierarchy
• Components can be nested and reused throughout an application

For example, we can split a header into its own Header component:

// Header.js

function Header(props) {
  return (
    <header>
      <h1>{props.title}</h1>
    </header>
  );
}

This Header component receives the title through props and can be reused by passing a title prop to it.

Introducing JSX

JSX is an XML/HTML-like syntax that gets compiled to JavaScript for rendering UI in React:

• Looks similar to HTML but has some key differences
• Full power of JavaScript available with curly braces
• camelCased props like className instead of class
• Self-closing tags required for elements like <img />

For example:

<header>
  <h1>Hello {name}!</h1>
</header>

This JSX mixes HTML markup with JavaScript code inside the curly braces.

Rendering Components

The ReactDOM.render() method mounts components to the DOM:

• Accepts a React element like <App /> as the first argument
• Renders that element to the target DOM node provided as second argument
• Components receive props from parents and render child components
• React handles updates when data changes using one-way binding

For example:

ReactDOM.render(
  <App />,
  document.getElementById('root')
);

This renders the App component into the DOM element with id 'root'.

Events and State

React components can handle events and manage state:

• onClick, onChange, onSubmit handlers respond to events
• useState hook declares state variables in function components
• Calling the state setter triggers a re-render when state changes
• Can lift state up to parent components instead of duplicating

For example:

function Counter() {
  const [count, setCount] = useState(0);

  return (
    <button onClick={() => setCount(count + 1)}>
      {count}
    </button>
  );
}

This component manages the count state to increment and update the UI when clicked.

State allows components to dynamically update in response to events and data changes.

React Hooks and State Management

React Hooks introduced a way to add stateful logic and lifecycle methods to function components. Some key hooks include useState, useEffect, useContext, and useReducer. For more complex apps, state management with Redux or MobX is helpful.

useState Hook

The useState hook declares state variables as an array with the variable and a setter function:

• Initialize with the default state value like const [count, setCount] = useState(0)
• Call setCount to update the count value
• Updates trigger a re-render of the component with latest state
• Can have multiple state slices with different useState calls

For example:

import { useState } from 'react';

function Counter() {
  const [count, setCount] = useState(0);

  function increment() {
    setCount(prevCount => prevCount + 1);
  }

  return (
    <div>
      <button onClick={increment}>Increment</button>
      <span>{count}</span>  
    </div>
  );
}

This component manages the count state variable to increment and display it.

useEffect Hook

This hook lets you run side effects after render like data fetching:

• Pass a callback function as the first argument
• Second optional arg controls when effect runs - on mount, update, unmount
• Useful for component lifecycle methods like componentDidMount
• Can return cleanup function to prevent memory leaks

For example:

useEffect(() => {
  // Fetch data on mount
  api.getData();
  
  // Cleanup
  return () => {
    // Cancel request on unmount 
  }
}, []);

This fetches data on mount and cleans up on unmount.

useContext Hook

The useContext hook provides access to React context in function components:

• Create context with React.createContext and default value
• Wrap tree with <MyContext.Provider value={data}> to provide context
• Components can access with const value = useContext(MyContext)
• Avoids passing props through all levels of component tree

For example:

const ThemeContext = React.createContext('light');

function App() {
  return (
    <ThemeContext.Provider value="dark">
      <Toolbar />
    </ThemeContext.Provider>
  );
}

function Toolbar() {
  const theme = useContext(ThemeContext);
  return (
    <div className={theme}>
      <button>Toggle Theme</button>
    </div>
  );
}

Any component in the tree can access the theme context.

Redux

For complex applications with significant state shared across components, Redux is a popular choice:

• External state management library often paired with React
• Unidirectional data flow and immutable state management
• Single centralized store accessed via connect() and actions
• React components subscribe to state changes they need

Advanced React Concepts

As you gain more experience with React, you'll encounter powerful patterns like higher-order components, render props, error handling, and suspense APIs.

Higher-Order Components

Higher-order components (HOCs) are advanced techniques in React for logic reuse:

• HOC is a function that takes a component and returns a new component
• They wrap a component to provide additional functionality
• Useful for abstracting common tasks into reusable functions
• Examples: connect() for Redux, withRouter() for React Router

For example:

// withAuth.js
function withAuth(Component) {
  return props => {
    // Check auth logic
    return <Component {...props} /> 
  }
}

This wraps components to handle auth logic.

Render Props

The render props pattern enables dynamic rendering logic sharing between components:

• Component receives a prop that's a render function returning JSX
• Lets components flexibly determine what content to render
• Useful for animations, data loading, styles, etc
• Avoids prop drilling or wrapping components

For example:

<DataFetcher render={data => <h1>{data.title}</h1>} />

DataFetcher fetches data and the render prop displays it.

Error Boundaries

Error boundaries allow you to gracefully handle React rendering errors:

• Defined with componentDidCatch lifecycle method
• Catches errors during rendering, in lifecycles, and child constructors
• Renders fallback UI when errors are caught
• Prevents whole app from crashing due to one error

React.lazy and Suspense

Lazy loading allows code splitting components into separate bundles:

• React.lazy takes a function that imports the component
• Suspense component displays a fallback while loading
• Useful for improving TTI (time-to-interactive)
• Can create granular loading states without Redux/Sagas

For example:

const OtherComponent = React.lazy(() => import('./OtherComponent'));

function MyComponent() {
  return (
    <Suspense fallback={<Loader />}>
      <OtherComponent />
    </Suspense>  
  );
}

OtherComponent is lazily loaded when rendered.

Conclusion

I hope this overview provides a solid introduction to learning React JS! We covered key concepts like components, props, state, JSX, hooks, routing, and state management that you'll need to build reactive user interfaces.

There is still much more to learn, but you should now feel comfortable diving into React resources like official docs, blogs, courses, and examples. Keep practicing building real-world apps and you'll continue improving as a React developer!

If you're looking for more interactive tutorials on learning React, be sure to check out Learn JavaScript for practical coding lessons and challenges.