Is HtmlUnit a good choice for scraping websites that heavily rely on JavaScript?

Yes, HtmlUnit can be a good choice for scraping websites that rely heavily on JavaScript. HtmlUnit is a "GUI-less browser for Java programs," which means it can simulate a web browser without a graphical user interface. This feature makes it suitable for tasks like automated testing and web scraping, especially for Java developers.

The key strengths of HtmlUnit for scraping JavaScript-heavy websites are:

1. JavaScript Support: HtmlUnit has built-in support for executing JavaScript, which means it can handle pages that require JavaScript to display content or execute AJAX calls. This enables HtmlUnit to interact with pages in a similar manner to how a real user would when using a standard web browser.

2. Configurability: It offers a high level of configurability, allowing you to customize how JavaScript is executed, manage cookies, set headers, and even use proxy servers.

3. Performance: Since it does not load a graphical interface, HtmlUnit can be faster than a traditional browser controlled through a browser automation framework like Selenium WebDriver.

4. Headless: It is inherently headless, so you don't need to set up a headless version of a browser such as Chrome or Firefox to run it in a headless environment (e.g., a server without a display).

Here is an example of how you might use HtmlUnit in Java to scrape a website:

import com.gargoylesoftware.htmlunit.WebClient;
import com.gargoylesoftware.htmlunit.html.HtmlPage;

public class HtmlUnitScraper {
    public static void main(String[] args) {
        // Create and configure WebClient
        try (final WebClient webClient = new WebClient()) {
            webClient.getOptions().setCssEnabled(false);
            webClient.getOptions().setJavaScriptEnabled(true);

            // Fetch the page
            final HtmlPage page = webClient.getPage("http://somejavascriptdependentwebsite.com");

            // Optionally wait for JavaScript to execute
            webClient.waitForBackgroundJavaScript(10000);

            // Get the page as XML (which is similar to HTML)
            final String pageAsXml = page.asXml();

            // Perform your scraping logic here
            System.out.println(pageAsXml);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

However, there are some considerations to keep in mind when deciding to use HtmlUnit:

• Complex JavaScript: If a website uses very complex or obscure JavaScript, HtmlUnit might not be able to execute it perfectly, as its JavaScript engine is not as advanced as those found in modern web browsers like Chrome or Firefox.

• Compatibility: Being a non-standard browser, there may be compatibility issues with some modern web applications that rely on features only supported by the major browsers.

• Maintenance: HtmlUnit is being maintained, but it's important to check its current status as libraries can become outdated or less supported over time.

• Learning Curve: If you are not familiar with Java, there will be a learning curve to use HtmlUnit effectively.

For Python developers, alternatives to HtmlUnit with JavaScript support include:

• Selenium: A browser automation tool that can be paired with headless browsers like Chrome or Firefox.
• Pyppeteer: A Python port of the Puppeteer library that controls headless Chrome or Chromium.
• Playwright for Python: A Python version of the Playwright library that allows automation of Chromium, Firefox, and WebKit with a single API.

Each of these options has its own set of pros and cons and should be chosen based on the specific requirements of your scraping project.