title: QWebEngine: How to get attribute value?
body: <p>I want to rewrite my project writen in <code>QWebView</code> to <code>QWebEngineView</code>, but I don't know how to get the attribute value and assign it to a C++ variable. I think that I should use <code>QWebEnginePage::runJavaScript</code> function. But I don't know how.</p>
  
  <p>For example, when I try to display value of element in console, I did this:</p>
  
  <pre><code>web-&gt;page()-&gt;runJavaScript("document.getElementById(\"login\").getAttribute(\"va‌​lue\")", []
  (QVariant result)-&gt;void {
      qDebug()&lt;&lt;result.toString();
  });
  </code></pre>
  
  <p>But It display nothing.</p>