jquery: flot chart - pan: how to do something on Dragstart

Question

I am using flot chart with pan (navigate js) option

<script src="{% static 'js/plugins/flot/jquery.flot.js' %}"></script>
<script src="{% static 'js/plugins/flot/jquery.flot.tooltip.min.js' %}"></script>
<script src="{% static 'js/plugins/flot/jquery.flot.resize.js' %}"></script>
<script src="{% static 'js/plugins/flot/jquery.flot.navigate.js' %}"></script>

Now when i start draging the chart i want to do something. How to do it.

I tried:

$(document).on("dragstart", ".flot-overlay", function(){
   alert("testing")
});

checked in the dom:

but its not working