Trying to detect when a dojo dijit splitter is dragged

Question

I am trying to detect when a dojo splitter is dragged. I'm not having any luck. Here's the code I'm using which isn't working.

require(["dojo/on", "dojo/dom", "dojo/ready", "dijit/registry","dojo/dom-construct", "dijit/layout/TabContainer", "dijit/layout/ContentPane",
  "dojo/dom-style"
], function(on, dom, ready, registry,domConstruct, TabContainer, ContentPane, domStyle) {
  ready(function() {
    console.log("dojo ready");
    var topsplitter =   dijit.registry.byId("top_splitter"); // Replace with your splitter's ID
    on(topsplitter, "drag", function (event) {
        console.log("Splitter dragged");
  });
  });
});