Web Scraping Next.js Sites: Harnessing React Hydration for Easy Data Extraction

Next.js has rapidly become one of the most popular frameworks for building modern web applications. According to a recent survey by Statista, Next.js ranks as the 5th most used web framework overall. Many leading companies rely on Next.js to power their websites and apps.

So what makes Next.js so appealing to developers? And what implications does its architecture have when it comes to web scraping? In this guide, we‘ll take a deep dive into Next.js and reveal a quick and easy technique for extracting data from sites built with this React framework. Let‘s get started!

Understanding the Next.js Architecture

At its core, Next.js is a React framework that enables server-side rendering (SSR) and generates static websites. It provides a powerful set of tools and optimized configurations that allow developers to easily create React applications.

When a user requests a page from a Next.js site, the framework pre-renders the page on the server into HTML. This server-side rendered HTML is then sent to the client browser. From the user‘s perspective, they immediately see a fully formed web page.

However, at this point, the page is not yet interactive. It‘s essentially a static HTML snapshot. To bring the page to life and enable dynamic React functionality, Next.js also sends a JavaScript bundle containing the React application code.

React Hydration: Bridging the Gap

Once the static HTML and React JavaScript bundle arrive in the browser, an essential process called hydration occurs. Hydration is the key to transforming the server-rendered HTML into a fully interactive React application.

During hydration, React takes the static HTML and attaches event listeners and state management to the appropriate components. It synchronizes the React application code with the existing HTML structure. This process allows React to efficiently reuse the server-rendered HTML while adding interactivity.

To perform hydration, React requires access to the same data that was used to render the page on the server. This is where Next.js introduces a clever solution. It injects a special script element into the HTML with an id of __NEXT_DATA__. This script contains a JSON object that holds the necessary data for hydration.

Here‘s an example of what the __NEXT_DATA__ script looks like:


<script id="__NEXT_DATA__" type="application/json">
{
"props": {
"pageProps": {
"data": {
"products": [
{
"id": 1,
"name": "Product 1",
"price": 19.99
},
{
"id": 2,
"name": "Product 2",
"price": 29.99
}
] }
}
}
}
</script>


As you can see, the __NEXT_DATA__ script contains a JSON object with a "props" field. Inside "props", you‘ll find the data passed to the page component during server-side rendering. This data is what React uses to hydrate the page and make it interactive.

Scraping Next.js Sites Using __NEXT_DATA__

Now that we understand how Next.js leverages React hydration and the role of the __NEXT_DATA__ script, let‘s explore how we can use this knowledge for web scraping.

Extracting data from a Next.js site becomes incredibly simple thanks to the __NEXT_DATA__ script. In fact, you can do it directly from your browser‘s developer tools without even writing a line of code!

Here‘s a step-by-step guide:

1. Open the desired page of the Next.js site you want to scrape in your web browser.

2. Right-click on the page and select "Inspect" to open the developer tools.

3. Switch to the "Console" tab in the developer tools.

4. Type the following command and press Enter:

   document.querySelector("#__NEXT_DATA__").textContent

   This command selects the __NEXT_DATA__ script element and retrieves its content.

5. You should now see the JSON data used for hydration printed in the console. It will include the data passed to the page component during server-side rendering.

6. To extract specific data fields, you can parse the JSON string and access the desired properties. For example, to get the "products" data from the previous example, you can use:

   
const jsonData = JSON.parse(document.querySelector("#__NEXT_DATA__").textContent);
console.log(jsonData.props.pageProps.data.products);


   This code parses the JSON string and logs the "products" array to the console.

That‘s it! You‘ve successfully scraped data from a Next.js site using the __NEXT_DATA__ script. You can now copy and paste the data into a file or process it further according to your needs.

Scraping Next.js Apps with self.__next_f.push

With the introduction of Next.js 13 and the new App Router, the hydration data is now passed differently. Instead of using the __NEXT_DATA script, Next.js injects multiple inline script elements that call the self.next_f.push function.

Here‘s an example of what these script elements look like:


<script>
self.next_f.push({
id: "__next_ssr-client-headers",
children: [{
"props": {
"products": [
{
"id": 1,
"name": "Product 1",
"price": 19.99
},
{
"id": 2,
"name": "Product 2",
"price": 29.99
}
] }
}] })
</script>


To scrape data from these script elements, you can use a slightly modified approach:

1. Open the developer tools and switch to the "Console" tab.

2. Use the following command to select all the script elements:

   const scriptElements = document.querySelectorAll("script");

3. Filter the script elements to find the one containing the desired data:

   
const dataElement = Array.from(scriptElements).find(element =>
element.innerText.includes("self.__next_f.push") &&
element.innerText.includes(‘"props"‘)
);


   This code searches for a script element that includes both the "self.__next_f.push" string and the "props" property.

4. Extract the JSON data from the script element:

   
const jsonString = dataElement.innerText.match(/{.*}/s)[0];
const jsonData = JSON.parse(jsonString);
console.log(jsonData.children[0].props);


   This code extracts the JSON object from the script element using a regular expression, parses it, and logs the "props" data.

While this approach requires a bit more effort compared to the __NEXT_DATA__ method, it still allows you to access the hydration data and extract valuable information from Next.js sites.

Limitations and Considerations

While scraping Next.js sites using the hydration data is relatively straightforward, there are a few limitations and considerations to keep in mind:

1. Partial Data: The hydration data only includes the initial data used to render the page on the server. If the page fetches additional data client-side using APIs or performs other dynamic operations, that data won‘t be present in the hydration script.

2. Manual Process: The techniques we discussed involve manually extracting the data using browser developer tools. To automate the scraping process, you would need to write a script that loads the page, retrieves the hydration data, and parses it programmatically.

3. Anti-Scraping Measures: Some websites employ anti-scraping techniques to prevent automated data extraction. These measures can include rate limiting, IP blocking, or using client-side rendering frameworks like React Native that don‘t expose the hydration data.

Simplifying Next.js Scraping with Bright Data

If you want to scrape Next.js sites at scale or need a more robust solution, consider using Bright Data‘s Web Unlocker. Web Unlocker is a powerful tool designed to handle the complexities of web scraping, including Next.js sites.

With Web Unlocker, you can easily retrieve the HTML content of any web page, regardless of the underlying framework or anti-scraping measures in place. It takes care of rendering JavaScript, handling CAPTCHAs, managing proxies, and more.

Using Web Unlocker, you can focus on extracting the data you need without worrying about the technical challenges of scraping Next.js sites. It provides a simple API that returns the rendered HTML, which you can then parse and process as needed.

Frequently Asked Questions

1. Can I remove or hide the NEXT_DATA script from the HTML?
   No, removing or hiding the NEXT_DATA script will break the React hydration process and lead to a non-functional page. The script is essential for Next.js to properly initialize the React application on the client-side.

2. Is it possible to prevent scraping of Next.js sites by removing the hydration data?
   While removing the hydration data may make scraping slightly more challenging, it‘s not a foolproof solution. Determined scrapers can still use headless browsers or tools like Bright Data‘s Web Unlocker to render and extract data from Next.js sites.

3. How can I detect if a website is built with Next.js?
   There are a few indicators that a website is built with Next.js:

   • Check for the presence of the __NEXT_DATA__ script in the HTML source code.
   • Look for script elements containing calls to self.__next_f.push.
   • Inspect the "X-Powered-By" header in the HTTP response, which may include "Next.js".

4. Are there other frameworks that use React hydration?
   Yes, React hydration is a common technique used by server-side rendering frameworks that work with React. Other frameworks that leverage hydration include Gatsby, Remix, and Razzle.

Conclusion

Next.js has revolutionized web development by combining the power of server-side rendering with the flexibility of React. Its architecture, which relies on React hydration, has inadvertently made it easier to scrape data from Next.js sites.

By leveraging the __NEXT_DATA script or the self.next_f.push calls, you can access the hydration data and extract valuable information without the need for complex scraping setups. However, it‘s essential to consider the limitations and potential anti-scraping measures in place.

For a more comprehensive and scalable solution, tools like Bright Data‘s Web Unlocker can simplify the process of scraping Next.js sites. It handles the rendering, bypasses anti-scraping techniques, and provides a clean HTML output for easy data extraction.

As Next.js continues to gain popularity, understanding its architecture and scraping techniques becomes increasingly valuable. By leveraging the insights shared in this guide, you can effectively extract data from Next.js sites and unlock new opportunities for your projects.