[SOLVED] UI Element Scrollbar Usage

You are probably looking for the set:scroll event that is fired on the Scroll View object: https://developer.playcanvas.com/en/api/pc.ScrollViewComponent.html#event:set:scroll

eg https://playcanvas.com/editor/scene/1056055

var Main = pc.createScript('main');
Main.attributes.add('scrollViewEntity', {type: 'entity'});

// initialize code called once per entity
Main.prototype.initialize = function() {
    this.scrollViewEntity.scrollview.on('set:scroll', function (position) {
        console.log(position);
    }, this);
};