Sharepoint2013 Modal Dialog won't load

Hi I have a simple page loaded into a SharePoint page library and trying to simulate a long run time without a full wait dialog. Below is the script that I have

<script type="text/javascript">
    var waitDialog = null;
    function DoWork() {
        toggleProcessingStatus(true);
        UpdateUI();
        toggleProcessingStatus(false);
    }
    function UpdateUI()
    {
        var lblControl = document.getElementById("lbl");
        for (i = 0; i < 20000; i++) 
        {            
            lblControl.innerText = lblControl.innerText + i;
        }
    }
    function toggleProcessingStatus(showStatus) {
        if (showStatus) {
            ExecuteOrDelayUntilScriptLoaded(ShowWaitDialog, "sp.js");
        }
        else {
            if (waitDialog != null) {
                //setTimeout(CloseWaitDialog, 5000);
                CloseWaitDialog();
            }
        }
    }
    function ShowWaitDialog() {
        waitDialog = SP.UI.ModalDialog.showWaitScreenWithNoClose('Updating...', 'Please wait while update completes...', 150, 330);
    }

    function CloseWaitDialog() {
        if (waitDialog != null) {
            waitDialog.close();
        }
    }
</script>
<input type="button" id="btnShowDialog" title="Do Long Running Work" name="Do Long Running Work" onclick="javascript: DoWork();" value="Do Long Running Work"/>
Label: <label id="lbl" title="Test">Test Wait Screen</label>

      

        
        
        
      

    

Any help is greatly appreciated.

Thank you, Mallikarjun