Monitor full page, non AJAX, requests to be notified

Recently, working on new charts and chart "exporting service" in JSF, I've faced a quite common problem. When you execute a long-running task (action), you would like to show a status "Please wait ..." dialog on start and close this dialog at the end, when the response arrives. This is not a problem for AJAX requests, but it is problematic for non AJAX requests which stream some binary content to the browser. To solve this issue, we can use the same technique as for instance the FileDownload component in PrimeFaces uses. We can set a special cookie in response and check this cookie periodically on the client-side if it is set. When this cookie is set, we can close the opened before dialog. The cookie can be set in JSF as

// set cookie to be able to ask it and close status dialog for example
FacesContext.getCurrentInstance().getExternalContext().addResponseCookie(
             "cookie.chart.exporting", "true", Collections.<String, Object>emptyMap());

Non AJAX button executes an JavaScript function, say monitorExporting, with two parameters which represent another JavaScript functions to be called at the beginning and the end of the request / response lifecycle.

<p:commandButton value="Export to PNG" ajax="false" action="#{combiChartController.exportToPng}"
             onclick="monitorExporting(start, stop)"/>

PrimeFaces already provides methods to check if cookies are enabled, to get and delete them. So, we can write

function monitorExporting(start, complete) {
    if(PrimeFaces.cookiesEnabled()) {
        if(start) {
           start();
        }
            
        window.chartExportingMonitor = setInterval(function() {
            var exportingComplete = PrimeFaces.getCookie('cookie.chart.exporting');
 
            if(exportingComplete === 'true') {
                if(complete) {
                    complete();
                }
                     
                clearInterval(window.chartExportingMonitor);
                PrimeFaces.setCookie('cookie.chart.exporting', null);
            }
        }, 150);
    }
}

The cookie is asked periodically with the setInterval(...). The function start shows the "Please wait ..." dialog and the function stop closes it.

<script type="text/javascript">
/* <![CDATA[ */
    function start() {
        statusDialog.show();
    }

    function stop() {
        statusDialog.hide();
    }
/* ]]> */
</script>

If cookies are disabled, nothing is shown of course, but it is normally a rare case.