HtmlUnit Exception

Question

I am having trouble understanding the meaning of this HTMLUnit Exception. It happens when I call click() on a link on a webpage.

Exception class=[net.sourceforge.htmlunit.corejs.javascript.WrappedException]
com.gargoylesoftware.htmlunit.ScriptException: Wrapped com.gargoylesoftware.htmlunit.ScriptException: TypeError: Cannot read property "offsetWidth" from null (http://webapps6.doc.state.nc.us/opi/scripts/DHTMLmessages.js#95) (javascript url#297)
at com.gargoylesoftware.htmlunit.javascript.JavaScriptEngine$HtmlUnitContextAction.run(JavaScriptEngine.java:534)
at net.sourceforge.htmlunit.corejs.javascript.Context.call(Context.java:537)
at net.sourceforge.htmlunit.corejs.javascript.ContextFactory.call(ContextFactory.java:538)
at com.gargoylesoftware.htmlunit.javascript.JavaScriptEngine.execute(JavaScriptEngine.java:432)
at com.gargoylesoftware.htmlunit.javascript.JavaScriptEngine.execute(JavaScriptEngine.java:407)
at com.gargoylesoftware.htmlunit.html.HtmlPage.executeJavaScriptIfPossible(HtmlPage.java:965)
at com.gargoylesoftware.htmlunit.html.HtmlAnchor.doClickAction(HtmlAnchor.java:87)
at com.gargoylesoftware.htmlunit.html.HtmlAnchor.doClickAction(HtmlAnchor.java:121)
at com.gargoylesoftware.htmlunit.html.HtmlElement.click(HtmlElement.java:1329)
at com.gargoylesoftware.htmlunit.html.HtmlElement.click(HtmlElement.java:1288)
at com.gargoylesoftware.htmlunit.html.HtmlElement.click(HtmlElement.java:1257)
at testapp.TestApp.main(TestApp.java:61)
Caused by: net.sourceforge.htmlunit.corejs.javascript.WrappedException: Wrapped com.gargoylesoftware.htmlunit.ScriptException: TypeError: Cannot read property "offsetWidth" from null (http://webapps6.doc.state.nc.us.js#95) (javascript url#297)
at net.sourceforge.htmlunit.corejs.javascript.Context.throwAsScriptRuntimeEx(Context.java:1802)
at net.sourceforge.htmlunit.corejs.javascript.MemberBox.invoke(MemberBox.java:196)
at net.sourceforge.htmlunit.corejs.javascript.FunctionObject.call(FunctionObject.java:479)
at net.sourceforge.htmlunit.corejs.javascript.Interpreter.interpretLoop(Interpreter.java:1701)
at net.sourceforge.htmlunit.corejs.javascript.Interpreter.interpret(Interpreter.java:854)
at net.sourceforge.htmlunit.corejs.javascript.InterpretedFunction.call(InterpretedFunction.java:164)
at net.sourceforge.htmlunit.corejs.javascript.ContextFactory.doTopCall(ContextFactory.java:429)
at com.gargoylesoftware.htmlunit.javascript.HtmlUnitContextFactory.doTopCall(HtmlUnitContextFactory.java:267)
at net.sourceforge.htmlunit.corejs.javascript.ScriptRuntime.doTopCall(ScriptRuntime.java:3183)
at net.sourceforge.htmlunit.corejs.javascript.InterpretedFunction.exec(InterpretedFunction.java:175)
at com.gargoylesoftware.htmlunit.javascript.JavaScriptEngine$5.doRun(JavaScriptEngine.java:423)
at com.gargoylesoftware.htmlunit.javascript.JavaScriptEngine$HtmlUnitContextAction.run(JavaScriptEngine.java:528)
... 11 more

Answer 1

When you click and this link call another page, htmlUnit can be very verbose on exceptions during navigation. If you click on your browser and open the console, probably will see those errors, missing links or images, errors on calling scripts..

Those are not necessary Javascript issues with HtmlUnit.

Like I said here HtmlUnit not creating HtmlPage object you can set or modify htmlUnit to prevent unecessary logs. You can also setup log4j and disable some exceptions.

So we use those options to keep html navegating without stoping on first error/problem we use :

webClient.getOptions().setThrowExceptionOnScriptError(false);
webClient.getOptions().setThrowExceptionOnFailingStatusCode(false);

You can also implement empty classes to stop htmlUnity go verbose on console about css/javaScript errors with:

webClient.setCssErrorHandler(new SilentCssErrorHandler());    
webClient.setJavaScriptErrorListener(new JavaScriptErrorListener(){});

The little sample test case:

@Test
public void TestCall() throws FailingHttpStatusCodeException, MalformedURLException, IOException {      
    WebClient webClient = new WebClient(BrowserVersion.CHROME);
    webClient.getOptions().setUseInsecureSSL(true); //ignore ssl certificate
    webClient.getOptions().setThrowExceptionOnScriptError(false);
    webClient.getOptions().setThrowExceptionOnFailingStatusCode(false);
    String url = "https://www.wearvr.com/#game_id=game_4";
    HtmlPage myPage = webClient.getPage(url);
    webClient.waitForBackgroundJavaScriptStartingBefore(200);
    webClient.waitForBackgroundJavaScript(20000);
    //do stuff on page ex: myPage.getElementById("main")
    //myPage.asXml() <- tags and elements
    System.out.println(myPage.asText());

} 

Also you can see more here Turning HtmlUnit Warnings off