Beyond the Basics: An In-Depth Exploration of Advanced ReactJS Techniques

Umur Alpay
24 May 2023


In the bustling world of front-end development, ReactJS has made a name for itself as an efficient, flexible, and powerful JavaScript library. Introduced by Facebook in 2013, it has rapidly become the library of choice for many developers and companies, thanks to its unique approach to building user interfaces and applications. This dominance is evident in the proliferation of its usage in the industry, from young tech startups to established Fortune 500 companies.

Yet, if you are reading this, you're likely already familiar with the elementary concepts of ReactJS. You've dipped your toes in the pool of JSX syntax, understand the mechanics of components, are comfortable with props, and have manipulated the state. Maybe you've even developed a few applications using create-react-app or ventured into managing state with Redux. But now, you yearn for something more, something beyond just the basics.

Welcome to "Beyond the Basics: An In-Depth Exploration of Advanced ReactJS Techniques". This is a series tailored for those who wish to expand their understanding, to delve deeper into ReactJS and to uncover the advanced aspects that lie beneath its surface.

Over the course of this series, we will navigate through complex and advanced ReactJS concepts such as Higher-Order Components (HOCs), Render Props, React Hooks, Context API, Suspense, React's Reconciliation Algorithm and Virtual DOM. We will also touch upon the best practices for performance optimization, testing, and structuring large-scale applications in React.

Admittedly, this journey will not be straightforward. We are venturing into areas that are intricate, nuanced, and sometimes abstract. But fear not, as the rewards are well worth the challenge. Armed with the knowledge from these advanced topics, you will be able to develop more efficient, maintainable, and scalable React applications.

Digging Deeper into ReactJS

Now that we've set the stage, let's dive headfirst into the depths of advanced ReactJS concepts. With our foundation in the basic building blocks of React, it's time to strengthen our understanding and expand our knowledge in areas that will not only make us more proficient developers but also allow us to write applications that are more performant, scalable, and maintainable.

Higher-Order Components (HOCs)

We begin our journey with Higher-Order Components, also known as HOCs. Inspired by the principles of higher-order functions in JavaScript, a HOC in React is a function that takes a component and returns a new component with additional props or behaviors. HOCs allow us to reuse component logic, which is particularly useful when you find yourself needing to share behaviors across multiple components. We'll delve into HOCs, exploring how they work, when to use them, and common pitfalls to avoid.

Render Props

Render props, another powerful pattern in React, involve a technique where a child component is supplied as a function to a parent component, allowing the child to determine what the parent will render. This pattern provides a flexible way for components to share dynamic state or logic. We will discuss why and when to use render props and see examples of how they make our components more flexible and reusable.

React Hooks

React Hooks, introduced in React 16.8, have reshaped the way we handle component state and side effects in functional components. Hooks allow us to write cleaner and more readable code, which was previously only possible in class-based components. We'll deep-dive into useState, useEffect, and other built-in hooks, and even explore writing our custom hooks for enhanced code reuse.

Context API

State management in React has historically been a challenging aspect, particularly for large applications. The Context API, a feature that allows us to share state and pass it through the component tree without having to pass props down manually at every level, is a godsend for handling global or shared state. We'll explore the ins and outs of this API and how it can simplify our state management.

Suspense and Concurrent Mode

React is not just about the creation of UIs; it's also about making them smooth and responsive for the end-user. This is where Suspense and Concurrent Mode come in. Suspense allows components to “wait” for something before rendering, while Concurrent Mode helps in rendering more complex user interfaces without blocking the main thread. We'll explore how to use these advanced features to improve user experience drastically.

React's Reconciliation and Virtual DOM

Finally, we'll dig into the heart of React's efficiency – the reconciliation algorithm and the virtual DOM. Understanding how React updates the DOM and optimizes rendering can provide critical insights for writing performant React applications. We'll dive into how the virtual DOM works and how the reconciliation algorithm helps React minimize actual DOM manipulations.

This exploration into the advanced aspects of ReactJS is akin to opening a treasure trove of wisdom and expertise. As we delve deeper, you will find that the more advanced facets of ReactJS not only make your codebase more robust but also provide a more profound understanding of how the library works, enhancing your problem-solving skills in the process. So let's continue on this journey, peeling back the layers of ReactJS, as we go Beyond the Basics.

Understanding the Component Lifecycle

React components have a life cycle akin to the stages of life for humans: birth, growth, and death. This life cycle can be categorized into three main phases: Mounting, Updating, and Unmounting. Understanding these phases, along with the specific methods that are called in each one, gives you more control over your components and can help improve the efficiency and performance of your applications.

Mounting: The Birth of Your Component

The mounting phase is the first stage of a component's life. This phase happens when the component is being created and inserted into the DOM. There are four methods that React calls in this phase:

constructor(): This method is the first that gets called. It’s where you initialize your component's state and bind event handlers.

static getDerivedStateFromProps(): This static method enables the component to update its state based on changes in props right before rendering.

render(): This is the method where you return your JSX. It's the only required method in a class component.

componentDidMount(): React calls this method right after the component has been rendered to the DOM, making it an excellent place for network requests.

Updating: Growth and Change

The update phase occurs when a component is re-rendered as a result of changes to either its props or state. React offers five methods during this phase:

static getDerivedStateFromProps(): Just like in the mounting phase, this method enables the component to update its state based on changes in props.

shouldComponentUpdate(): This lifecycle method allows your component to exit the update life cycle if there is no reason to apply a new render.

render(): The component gets rendered.

getSnapshotBeforeUpdate(): This method enables your component to capture some information from the DOM before it is potentially changed.

componentDidUpdate(): This method is called right after the render method. It's a great place to perform network requests as long as you compare the current props to previous ones.

Unmounting: The End of the Component Life

The unmounting phase is the final stage of a component's life cycle. This phase occurs when the component is being removed from the DOM. React offers one method in this phase:

  • componentWillUnmount(): This method is called immediately before a component is destroyed and removed from the DOM. It’s used for cleanup purposes (like invalidating timers, canceling network requests, or cleaning up any subscriptions that were created in componentDidMount()).

Understanding and utilizing these lifecycle methods appropriately can lead to efficient code that is easy to manage and debug. It's like having a detailed roadmap of your component's journey from creation to destruction, providing you with hooks where you can plug in your code at just the right time.

Moving forward, remember that as of React 16.3, some lifecycle methods have been deprecated in favor of new ones. It's always a good idea to check the official React documentation to keep up with the latest practices. In the next part of this series, we will dive deeper into newer features like React Hooks, which can help us write more intuitive and functional component code, greatly simplifying the component lifecycle.

ReactJS Hooks

One of the most significant recent evolutions in React has been the introduction of Hooks. Introduced in React 16.8, Hooks fundamentally changed the way we write React components, allowing us to use state and other React features without writing a class.

The Power of useState

The useState Hook is at the core of functional components. This Hook allows you to add state to your functional components, just like this.state in a class component. The useState Hook takes one argument, the initial state, and returns an array with the current state and a function to update it. For instance:

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

In this case, count is the current state, setCount is the function to update the state, and 0 is the initial state.

The Flexibility of useEffect

While useState manages state, useEffect manages side effects. It serves the same purpose as componentDidMount, componentDidUpdate, and componentWillUnmount in React classes. The useEffect Hook allows you to perform side effects in function components. These side effects could be data fetching, setting up a subscription, or manually changing the DOM. For example:

useEffect(() => {
    document.title = `You clicked ${count} times`;
}, [count]); 

In this example, we’re updating the document title after React updates the DOM, and the second parameter ([count]) means this useEffect will run whenever count changes.

Crafting Custom Hooks

Beyond useState and useEffect, React allows you to create your custom Hooks. Custom Hooks are a mechanism to reuse stateful logic, not state itself. With custom Hooks, you can extract component logic into reusable functions. For instance, you could create a custom Hook to fetch and manage data:

function useDataFetch(url) {
    const [data, setData] = useState(null);
    const [loading, setLoading] = useState(true);
    useEffect(() => {
      async function fetchData() {
        const response = await fetch(url);
        const data = await response.json();
    }, [url]);
    return { data, loading };

With this custom Hook, any component can now easily fetch and use data.

The Simplicity of useContext

Another powerful Hook, useContext, allows you to avoid prop-drilling and easily access the context data without wrapping your component in a Consumer. It makes the usage of context much easier and cleaner:

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

In this example, useContext takes a context object and returns the current context value, in this case, 'light'.

React Hooks provide a powerful and elegant way to handle state and side effects in your functional components, and by creating custom Hooks, you can leverage their power even more by extracting component logic into reusable functions. Hooks represent a shift in how we write React and enable us to compose our components in a more intuitive and easier-to-understand manner.

Advanced State Management

As applications grow and become more complex, managing state in a clear, predictable manner becomes crucial. Although React's built-in state management capabilities can handle a fair amount of complexity, you might find yourself needing something more robust. This is where advanced state management techniques and libraries, such as Redux, MobX, and the Context API, come into play.

The Predictability of Redux

Redux is a predictable state container designed to help you write JavaScript applications that behave consistently across different environments. The core philosophy behind Redux is that the entire state of your application is stored in one central location, known as the store. Any changes to this state are made through actions and reducers, making your state changes predictable and easy to trace.

Redux also comes with a variety of middleware options that can handle side effects and asynchronous actions, such as Redux Thunk and Redux Saga. Additionally, its devtools extension provides an excellent UI for debugging, allowing you to track every action and state change in your application.

The Simplicity of MobX

MobX, on the other hand, takes a slightly different approach. Rather than having a single store and explicit actions, MobX allows you to create observable state variables across your application and automatically tracks what components are using which state variables. When a state variable changes, any component that uses that variable is automatically re-rendered.

This makes MobX incredibly simple and intuitive to use, especially for smaller applications. However, the trade-off is that your state changes aren't as explicit as Redux, and larger applications may be more difficult to debug and manage.

The Flexibility of the Context API

Finally, let's talk about the Context API. The Context API is built directly into React and allows you to create global state variables that can be passed down to any child component via context, without the need for prop drilling.

You can think of context as a way to pass state through the component tree without having to pass props down manually at every level. The useContext Hook further simplifies its usage by allowing you to use context in functional components without wrapping them in a Consumer.

For smaller applications or ones that don't need the full power of Redux or MobX, the Context API is an excellent choice. It provides just enough state management for many common use cases, without the additional complexity that comes with Redux and MobX.

In the end, choosing the right state management strategy depends on your specific needs and the complexity of your application. Redux offers predictability and excellent tooling, MobX provides simplicity and intuitiveness, while the Context API offers flexibility without the need for additional libraries.

Higher-Order Components (HOCs) and Render Props

As you deepen your understanding of React, you're bound to come across some design patterns that are commonly used in larger, more complex applications. Among these patterns, Higher-Order Components (HOCs) and Render Props stand out as key concepts that can greatly enhance your React toolkit. Both patterns allow you to share common functionality across multiple components. Let's dive in.

Exploring Higher-Order Components

In React, a Higher-Order Component (HOC) is a function that takes a component and returns a new component with additional props or behaviors. HOCs are a way to reuse component logic, which can be particularly useful in larger applications where you may need to share certain behaviors across multiple components.

Here's a simple example of a HOC that adds a width prop to any component:

function withWindowWidth(Component) {
    return function WrappedComponent(props) {
        const [width, setWidth] = useState(window.innerWidth);

        useEffect(() => {
            const handleResize = () => setWidth(window.innerWidth);
            window.addEventListener('resize', handleResize);
            return () => {
                window.removeEventListener('resize', handleResize);
        }, []);

        return <Component {...props} width={width} />;

The withWindowWidth HOC can now be used to add a width prop to any component:

const MyComponentWithWidth = withWindowWidth(MyComponent);

Understanding Render Props

While HOCs are a powerful pattern, they do have some pitfalls - they can be confusing when dealing with prop naming collisions, and they can lead to "wrapper hell" with too many nested HOCs. This is where Render Props come in.

The term "render prop" refers to a technique where a function prop that a component uses to know what to render. Instead of implicitly sharing behavior like HOCs, Render Props make sharing explicit...right in the render method!

Here's a similar example to the above, but using Render Props instead:

class WindowWidth extends React.Component {
    state = { width: window.innerWidth };

    handleResize = () => this.setState({ width: window.innerWidth });

    componentDidMount() {
        window.addEventListener('resize', this.handleResize);

    componentWillUnmount() {
        window.removeEventListener('resize', this.handleResize);

    render() {
        return this.props.render(this.state.width);

You can then use this WindowWidth component in your render method, like so:

<WindowWidth render={width => <div>Window width is {width}</div>} />

In this case, the WindowWidth component is responsible for attaching and cleaning up the resize event listener, while the component using it can decide how to use the width value in its render method.

HOCs and Render Props: Powerful Patterns

Both Higher-Order Components and Render Props are powerful patterns for sharing component logic in a React application. While they can seem a bit abstract at first, getting comfortable with these patterns can greatly improve the clarity and reusability of your code.

React Router and Navigation

In single-page applications (SPAs), routing is a core concept, and React Router is one of the most popular libraries to handle it in React. Routing helps in navigating through the application and maintains the user interface's state when moving between different views or pages. React Router keeps your UI in sync with the URL, creating a seamless user experience.

Basic Routing with React Router

At its heart, React Router is a set of components. For example, to create different "pages" in your app, you would wrap each page in a Route component:

import { BrowserRouter as Router, Route } from "react-router-dom";

  <Route path="/about" component={AboutPage} />
  <Route path="/contact" component={ContactPage} />
  <Route path="/home" component={HomePage} />

In this example, when the user navigates to /about, the AboutPage component would be rendered.

Nested and Dynamic Routing

React Router also supports nested and dynamic routing. Nested routing allows you to create more complex UIs, where a section of your app has its routes and views. Dynamic routing allows you to create routes that match patterns, rather than exact paths. For example, if you had a blog and wanted to create a route for each blog post, you could do this:

<Route path="/post/:id" component={BlogPost} />

In this case, :id is a URL parameter, and its actual value will be passed to the BlogPost component as a prop.

Navigation between pages is done with the Link and NavLink components, which render as <a> tags in the DOM but prevent the default browser action of a page reload.

import { Link } from "react-router-dom";

<Link to="/about">About</Link>

NavLink is a special type of Link that can apply styles to the active route, making it easy to give users visual feedback of their current location in the app.

Redirects and 404 pages

React Router provides Redirect for redirection from one route to another. This is useful when you want to redirect a user after an action or based on a condition:

<Route exact path="/">
  {loggedIn ? <Redirect to="/dashboard" /> : <PublicHomePage />}

To handle 404 or not found pages, you can use a Route with no path prop, which will always match:

<Route component={NotFoundPage} />

This Route should always be the last one because the router will select the first Route or Redirect that matches the current location.

React Router is an effective library for handling navigation in React applications, allowing you to create single-page applications with multiple views, dynamic and nested routes, all while keeping the URL and UI in sync.

Optimizing React Applications

React is well-loved for its simplicity and ease of use, but as applications scale, developers may encounter performance issues. Fortunately, React provides several techniques for optimizing an application's performance.

Avoiding Unnecessary Rerenders with shouldComponentUpdate and React.memo

React components rerender by default whenever their parent rerenders or whenever state or props change. In many cases, this is exactly what you want. But sometimes, a component's rerender doesn't actually change the DOM, leading to unnecessary computation.

Class components can implement the shouldComponentUpdate lifecycle method to control rerendering. If shouldComponentUpdate returns false, the component won't rerender, saving rendering time. However, use this with caution: if done incorrectly, it could lead to bugs where your UI doesn't update to reflect the underlying data.

For function components, a similar optimization is available through React.memo. If a component is wrapped in React.memo, it will only rerender if its props change. This can be particularly useful for "leaf" components near the bottom of your component hierarchy.

Profiling with the DevTools Profiler

React DevTools offers a profiler that lets you see exactly when and why your components are rerendering. You can see a flame graph of render times, inspect the props and state of a component at any point in time, and even see why a component rerendered: due to a props change, state change, or context change.

Optimizing Context with useMemo and useCallback

React's Context API is a powerful way to share data across your component hierarchy. But, it has a potential performance problem: when context data changes, all components consuming that context will rerender. If you're storing multiple values in context, a change to one value will cause rerenders due to other values, even if they didn't change.

The solution is to split your context into multiple pieces, each holding one value. That way, a component can consume only the piece of context it needs, and it won't rerender due to changes in other values.

This can be paired with useMemo or useCallback to avoid unnecessary computations. useMemo returns a memoized value, only recalculating it when one of its dependencies change. useCallback is similar, but it returns a memoized function.

Code Splitting with React.lazy

As applications grow, so does the bundle size, leading to increased load times. Code-splitting is a technique that allows you to split your code into smaller chunks which you can then load on demand.

React provides a built-in way to use code-splitting through the React.lazy function. It allows you to render a dynamic import as a regular component.

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

function MyComponent() {
  return (
      <React.Suspense fallback={<div>Loading...</div>}>
        <OtherComponent />

In this example, OtherComponent will be loaded only when it's needed for the render.

Mastering performance optimization techniques in React is a crucial step in becoming an advanced React developer. These techniques help ensure your application not only works well but feels snappy and responsive to the user.

Server-Side Rendering with React (SSR)

Server-side rendering (SSR) is a popular technique for rendering a client-side single page application (SPA) on the server and sending a fully rendered page to the client. The client's JavaScript bundle can then take over and the SPA can operate as normal.

SSR offers several benefits including improved performance on mobile and low-powered devices, a faster first contentful paint, and better SEO as web crawlers can better understand your content.

React and Node.js: A Match Made in SSR Heaven

React is a library for building user interfaces, and while it's typically run in the browser, it can also be run on the server with Node.js. This makes React an ideal library for building universal JavaScript applications where the same code can run on both the client and the server.

To enable SSR with React, you need to use the renderToString or renderToNodeStream function from react-dom/server. These functions take your React tree, render it to HTML, and then send it to the client.

Here's an example of a simple server-side rendered React app using Express:

import express from 'express';
import React from 'react';
import ReactDOMServer from 'react-dom/server';
import App from './App';

const app = express();

app.get('/', (req, res) => {
  const html = ReactDOMServer.renderToString(<App />);

    <!DOCTYPE html>
        <title>My SSR App</title>
        <script src="/bundle.js" defer></script>
        <div id="root">${html}</div>


Handling Data Fetching

Data fetching in a server-rendered app can be a bit tricky. You need to ensure that all data for your components is loaded before you call renderToString. Otherwise, your HTML will not be fully populated when it's sent to the client.

You might have components that fetch data in a useEffect hook, which doesn't run when rendering on the server. One solution to this is to use a library like react-query or apollo-client that supports prefetching data on the server.

Routing with SSR

When dealing with SSR, handling routing is another challenge. You want your server to be able to respond to any route that your React application can handle. This requires a server-side router that can match the routes of your client-side application.

You can use the StaticRouter component from react-router-dom to render your routes on the server. StaticRouter is similar to BrowserRouter, but it's designed for server-side rendering scenarios.

SEO and Performance Benefits

One of the biggest advantages of SSR is its potential improvement to SEO. As your application is fully rendered when it reaches the search engine crawlers, it allows these crawlers to better understand your site's content.

Performance, particularly on mobile and low-powered devices, is another reason to consider SSR. It allows you to leverage the server's computational power to do the initial rendering, saving precious milliseconds of parsing and execution time on the client.

In summary, Server-Side Rendering with React offers many benefits and can improve your application's performance, SEO, and user experience.

Unit Testing in React

As a React developer, testing your components is paramount to ensure that your application is running as expected and to prevent bugs from making it to production. Luckily, the React ecosystem provides a variety of tools to facilitate this testing process.

Getting Started: Jest and React Testing Library

The main tools for testing React components are Jest and React Testing Library. Jest is a JavaScript testing framework that provides a full suite of testing functionality, including a test runner, assertion library, and mock/spy functionality. React Testing Library is a set of utilities that allows you to test React components in a way that closely resembles how they're used in a real browser.

Installing these tools is as simple as running npm install --save-dev jest @testing-library/react.

Writing Your First Test

When writing tests, you want to test the behavior of your component, not its implementation details. This philosophy is the core tenet of React Testing Library.

Let's suppose we have a simple Counter component:

import React, { useState } from "react";

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

  return (
      <p>You clicked {count} times</p>
      <button onClick={() => setCount(count + 1)}>Click me</button>

export default Counter;

Here is an example of how to test it:

import { render, fireEvent } from "@testing-library/react";
import Counter from "./Counter";

test("Counter increments the count", () => {
  const { getByText } = render(<Counter />);

  const button = getByText("Click me");;;

  expect(getByText("You clicked 2 times")).toBeTruthy();

In this test, we render the Counter component, simulate two button clicks, and then assert that the displayed count increased to 2.

Testing Asynchronous Behavior

React Testing Library includes a family of waitFor functions to handle any asynchronous behavior in your components. These functions will repeatedly execute their callback until it doesn't throw an error or a timeout is reached.

Consider a component that fetches some data on mount and displays it. Here's an example of how you might test that:

import { render, waitFor } from "@testing-library/react";
import axios from 'axios';
import User from './User';


test("User component fetches and displays data", async () => {
  axios.get.mockResolvedValue({ data: { name: "John Doe" } });

  const { getByText } = render(<User userId={1} />);

  await waitFor(() => getByText("John Doe"));

  expect(getByText("John Doe")).toBeTruthy();

In this test, we use Jest's mocking capabilities to mock axios, our HTTP library. We then use waitFor to wait until our component has finished fetching the data and updated its state.

Unit testing is a key aspect of development and provides confidence in your application's functionality. By writing robust unit tests, you can catch bugs early, refactor with confidence, and ensure your application is working as expected.

Conclusions and Best Practices

As we bring our deep dive into advanced ReactJS techniques to a close, it's important to take a step back and reflect on the overarching principles that make React such a powerful and flexible tool for building user interfaces.

React's power lies in its component-based architecture, the unidirectional data flow, and the seamless interactivity it brings to web applications. As we've discovered, advanced concepts like hooks, context API, higher-order components, and render props enable us to leverage these principles to build complex, stateful components with less code and greater clarity.

Here are some key takeaways and best practices that we've touched upon:

Master the basics: Before diving into advanced topics, ensure you have a strong grasp of the basics, including JSX, components, state, props, and the component lifecycle.

Embrace composition: React is all about component composition. Don’t be afraid to break down your UI into smaller, reusable components. This will make your code more readable, maintainable, and testable.

Keep components small and focused: Each component should ideally have a single responsibility. If a component grows too large or complex, consider breaking it down into smaller sub-components.

Understand and use hooks effectively: Hooks simplify state management in functional components. Get comfortable with useState and useEffect before moving on to more advanced hooks like useMemo, useCallback, and useContext.

Stay up to date with the community and ecosystem: The React ecosystem is always evolving. Keep an eye on the official React blog, GitHub, and social media to stay informed about the latest developments.

Testing is crucial: Automated testing helps you catch bugs, improve code quality, and develop with confidence. Get comfortable with testing libraries like Jest and React Testing Library, and aim for a good level of test coverage in your applications.

Performance matters: As your application grows, consider performance optimizations to keep it snappy. Techniques like memoization, lazy loading, and server-side rendering can make a big difference.

Write clean, readable code: Prioritize writing code that is clean and easy to understand over clever, concise code. Remember, code is read far more often than it is written.

By adhering to these best practices and continually honing your skills, you will be well on your way to mastering React and building efficient, scalable web applications.

I hope you've found this series, "Beyond the Basics: An In-Depth Exploration of Advanced ReactJS Techniques," insightful and enriching. Remember, the key to becoming proficient in any technology is consistent practice and a deep curiosity to learn. Keep building, keep exploring, and most importantly, enjoy the process.

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