reimplement the shouldInterruptJavaScript() in Qt (C++)

All the info you need is in the documentation.

Create a new custom class that inherits from QWebPage, make sure it's a Q_OBJECT to receive signals.

class MyFunkyPage : public QWebPage {
    Q_OBJECT
public slots:
    bool shouldInterruptJavaScript() {
        QApplication::processEvents(QEventLoop::AllEvents, 42);
        // Ignore the error
        return false;
    }
};

Set the page of your QWebView to a custom subclass of QWebPage.

setPage(new MyFunkyPage());

Then when your page gets this signal it won't stop the script from executing, and it won't show a dialog.

The MyFunkyPage solution potentially leaks memory and causes crashes because the object passed to setPage has no parent and setPage does not take ownership. Instead,

class QWebPageWithoutJsWarning : public QWebPage {
    Q_OBJECT
public:
    QWebPageWithoutJsWarning(QObject* parent = 0) : QWebPage(parent) {}
public slots:
    bool shouldInterruptJavaScript() {
        return false;
    }
};

Set the page of your QWebView to the custom subclass of QWebPage, parented on the WebView,

void suppressJSWarning(QWebView& webView) {
    webView.setPage(new QWebPageWithoutJsWarning(&webView));
}

@anson-mackeracher almost had it right.

Qt needs it to be a private slot, not a public one. Here's what works for my class:

class MyFunkyPage : public QWebPage {
  Q_OBJECT

private slots:
  bool shouldInterruptJavaScript() {
    // Ignore the error  (return true to kill the runaway JavaScript)
    return false;
  }
};

Set the page of your QWebView to a custom subclass of QWebPage.

setPage(new MyFunkyPage());

I just tested this with Qt 4.8.4 and it works like a charm. I didn't need the processEvents call.