Mermaid Js not loaded

Start by reproducing the supplied HtmlUnitDriver test with the Mermaid CDN script and the shown HtmlUnit 3 driver dependency. Check how external scripts are fetched and executed for a data: URL, then compare the observed behavior with the reported missing mermaid global. Done means the cause is identified and a regression test demonstrates the corrected behavior; the issue does not name repository files or tests.

public static void testMermaidRendering() throws IOException, InterruptedException {
   HtmlUnitDriver driver = DriverPool.borrowDriver();

   String html = """
       <!DOCTYPE html>
       <html>
       <head>
           <meta charset="utf-8">
           <title>Mermaid Rendering Test</title>
           <!-- Load actual Mermaid library from CDN -->
           <script src="https://cdn.jsdelivr.net/npm/mermaid@10/dist/mermaid.min.js"></script>
           <style>
               .mermaid { font-family: sans-serif; }
           </style>
       </head>
       <body>
           <div class="mermaid">
               graph TD
               A[Start] --> B[Process]
               B --> C{Decision}
               C -->|Yes| D[Result 1]
               C -->|No| E[Result 2]
           </div>
           
           <script>
               mermaid.initialize({
                   startOnLoad: true,
                   theme: 'default',
                   flowchart: {
                       useMaxWidth: false,
                       htmlLabels: true
                   }
               });
           </script>
       </body>
       </html>
       """;

   // Load the page
   driver.get("data:text/html;charset=UTF-8," + html);

   // Wait for Mermaid to render (may need longer wait for actual network request)
   Thread.sleep(3000);

   // Verify rendering results
   WebElement mermaidContainer = driver.findElement(By.cssSelector(".mermaid"));
   System.out.println("Mermaid container HTML:\n" + mermaidContainer.getAttribute("outerHTML"));

   // Check for SVG elements
   List<WebElement> svgElements = mermaidContainer.findElements(By.tagName("svg"));
   System.out.println("Number of SVG elements found: " + svgElements.size());

   // Print the rendered diagram's text content
   String diagramText = (String) driver.executeScript(
       "return document.querySelector('.mermaid').textContent");
   System.out.println("Diagram text content: " + diagramText.trim());

   driver.quit();
 }


   public static HtmlUnitDriver borrowDriver() {
     HtmlUnitDriver htmlUnitDriver = new HtmlUnitDriver(BrowserVersion.CHROME, true);
     htmlUnitDriver.getWebClient().setCssErrorHandler(new SilentCssErrorHandler());
     htmlUnitDriver.getWebClient().getOptions().setFetchPolyfillEnabled(true);
//      htmlUnitDriver.getWebClient().getOptions().setThrowExceptionOnScriptError(false);
     htmlUnitDriver.getWebClient().getOptions().setCssEnabled(true);
     return htmlUnitDriver;
   }

I'm using

<dependency>
      <groupId>org.seleniumhq.selenium</groupId>
      <artifactId>htmlunit3-driver</artifactId>
      <version>4.32.0</version>
    </dependency>

I'm getting the following exception

Exception in thread "main" org.openqa.selenium.WebDriverException: org.htmlunit.ScriptException: ReferenceError: "mermaid" is not defined. (script in data:text/html;charset=UTF-8,<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>Mermaid Rendering Test</title>
    <!-- Load actual Mermaid library from CDN -->
    <script src="https://cdn.jsdelivr.net/npm/mermaid@10/dist/mermaid.min.js"></script>
    <style>
        .mermaid { font-family: sans-serif; }
    </style>
</head>
<body>
    <div class="mermaid">
        graph TD
        A[Start] --> B[Process]
        B --> C{Decision}
        C -->|Yes| D[Result 1]
        C -->|No| E[Result 2]
    </div>

    <script>
        mermaid.initialize({
            startOnLoad: true,
            theme: 'default',
            flowchart: {
                useMaxWidth: false,
                htmlLabels: true
            }
        });
    </script>
</body>
</html> from (21, 13) to (30, 14)#22)
Build info: version: '4.31.0', revision: '1ef9f18787*'
System info: os.name: 'Mac OS X', os.arch: 'aarch64', os.version: '15.2', java.version: '17.0.10'
Driver info: driver.version: HtmlUnitDriver
	at org.openqa.selenium.htmlunit.HtmlUnitDriver.get(HtmlUnitDriver.java:665)
	at org.openqa.selenium.htmlunit.HtmlUnitDriver.lambda$get$7(HtmlUnitDriver.java:619)
	at org.openqa.selenium.htmlunit.HtmlUnitDriver.lambda$runAsync$0(HtmlUnitDriver.java:351)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
	at java.base/java.lang.Thread.run(Thread.java:842)
Caused by: org.htmlunit.ScriptException: ReferenceError: "mermaid" is not defined. (script in data:text/html;charset=UTF-8,<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>Mermaid Rendering Test</title>
    <!-- Load actual Mermaid library from CDN -->
    <script src="https://cdn.jsdelivr.net/npm/mermaid@10/dist/mermaid.min.js"></script>
    <style>
        .mermaid { font-family: sans-serif; }
    </style>
</head>
<body>
    <div class="mermaid">
        graph TD
        A[Start] --> B[Process]
        B --> C{Decision}
        C -->|Yes| D[Result 1]
        C -->|No| E[Result 2]
    </div>

    <script>
        mermaid.initialize({
            startOnLoad: true,
            theme: 'default',
            flowchart: {
                useMaxWidth: false,
                htmlLabels: true
            }
        });
    </script>
</body>
</html> from (21, 13) to (30, 14)#22)
	at org.htmlunit.javascript.JavaScriptEngine$HtmlUnitContextAction.run(JavaScriptEngine.java:934)
	at org.htmlunit.corejs.javascript.Context.call(Context.java:627)
	at org.htmlunit.corejs.javascript.ContextFactory.call(ContextFactory.java:448)
	at org.htmlunit.javascript.HtmlUnitContextFactory.callSecured(HtmlUnitContextFactory.java:312)
	at org.htmlunit.javascript.JavaScriptEngine.execute(JavaScriptEngine.java:781)
	at org.htmlunit.javascript.JavaScriptEngine.execute(JavaScriptEngine.java:756)
	at org.htmlunit.html.HtmlPage.executeJavaScript(HtmlPage.java:949)
	at org.htmlunit.html.ScriptElementSupport.executeInlineScriptIfNeeded(ScriptElementSupport.java:347)
	at org.htmlunit.html.ScriptElementSupport.executeScriptIfNeeded(ScriptElementSupport.java:213)
	at org.htmlunit.html.ScriptElementSupport$1.execute(ScriptElementSupport.java:112)
	at org.htmlunit.html.ScriptElementSupport.onAllChildrenAddedToPage(ScriptElementSupport.java:131)
	at org.htmlunit.html.HtmlScript.onAllChildrenAddedToPage(HtmlScript.java:216)
	at org.htmlunit.html.parser.neko.HtmlUnitNekoDOMBuilder.endElement(HtmlUnitNekoDOMBuilder.java:514)
	at org.htmlunit.cyberneko.xerces.parsers.AbstractSAXParser.endElement(AbstractSAXParser.java:287)
	at org.htmlunit.html.parser.neko.HtmlUnitNekoDOMBuilder.endElement(HtmlUnitNekoDOMBuilder.java:460)
	at org.htmlunit.cyberneko.HTMLTagBalancer.callEndElement(HTMLTagBalancer.java:1254)
	at org.htmlunit.cyberneko.HTMLTagBalancer.endElement(HTMLTagBalancer.java:1198)
	at org.htmlunit.cyberneko.filters.DefaultFilter.endElement(DefaultFilter.java:169)
	at org.htmlunit.cyberneko.filters.NamespaceBinder.endElement(NamespaceBinder.java:264)
	at org.htmlunit.cyberneko.HTMLScanner$ContentScanner.scanEndElement(HTMLScanner.java:3223)
	at org.htmlunit.cyberneko.HTMLScanner$ContentScanner.scan(HTMLScanner.java:2133)
	at org.htmlunit.cyberneko.HTMLScanner.scanDocument(HTMLScanner.java:930)
	at org.htmlunit.cyberneko.HTMLConfiguration.parse(HTMLConfiguration.java:350)
	at org.htmlunit.cyberneko.HTMLConfiguration.parse(HTMLConfiguration.java:308)
	at org.htmlunit.cyberneko.xerces.parsers.AbstractXMLDocumentParser.parse(AbstractXMLDocumentParser.java:79)
	at org.htmlunit.html.parser.neko.HtmlUnitNekoDOMBuilder.parse(HtmlUnitNekoDOMBuilder.java:757)
	at org.htmlunit.html.parser.neko.HtmlUnitNekoHtmlParser.parse(HtmlUnitNekoHtmlParser.java:178)
	at org.htmlunit.DefaultPageCreator.createHtmlPage(DefaultPageCreator.java:300)
	at org.htmlunit.DefaultPageCreator.createPage(DefaultPageCreator.java:219)
	at org.htmlunit.WebClient.loadWebResponseInto(WebClient.java:690)
	at org.htmlunit.WebClient.loadWebResponseInto(WebClient.java:584)
	at org.htmlunit.WebClient.getPage(WebClient.java:501)
	at org.htmlunit.WebClient.getPage(WebClient.java:410)
	at org.openqa.selenium.htmlunit.HtmlUnitDriver.get(HtmlUnitDriver.java:638)
	... 5 more
Caused by: org.htmlunit.corejs.javascript.EcmaError: ReferenceError: "mermaid" is not defined. (script in data:text/html;charset=UTF-8,<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>Mermaid Rendering Test</title>
    <!-- Load actual Mermaid library from CDN -->
    <script src="https://cdn.jsdelivr.net/npm/mermaid@10/dist/mermaid.min.js"></script>
    <style>
        .mermaid { font-family: sans-serif; }
    </style>
</head>
<body>
    <div class="mermaid">
        graph TD
        A[Start] --> B[Process]
        B --> C{Decision}
        C -->|Yes| D[Result 1]
        C -->|No| E[Result 2]
    </div>

    <script>
        mermaid.initialize({
            startOnLoad: true,
            theme: 'default',
            flowchart: {
                useMaxWidth: false,
                htmlLabels: true
            }
        });
    </script>
</body>
</html> from (21, 13) to (30, 14)#22)
	at org.htmlunit.corejs.javascript.ScriptRuntime.constructError(ScriptRuntime.java:5312)
	at org.htmlunit.corejs.javascript.ScriptRuntime.constructError(ScriptRuntime.java:5293)
	at org.htmlunit.corejs.javascript.ScriptRuntime.notFoundError(ScriptRuntime.java:5416)
	at org.htmlunit.corejs.javascript.ScriptRuntime.name(ScriptRuntime.java:2194)
	at org.htmlunit.corejs.javascript.Interpreter.interpretLoop(Interpreter.java:2105)
	at org.htmlunit.corejs.javascript.Interpreter.interpret(Interpreter.java:1161)
	at org.htmlunit.corejs.javascript.InterpretedFunction.call(InterpretedFunction.java:92)
	at org.htmlunit.corejs.javascript.ContextFactory.doTopCall(ContextFactory.java:356)