load on demand in TreeList

Hi, Andrei,

Load on demand can be achieved inside the onExpandChange event since it provides a level prop (an array that has all the indexes of the parent items). It can be used inside the getItemPath function which returns the expanded node and the parent. This way by obtaining the expanded `dataItem` you can make a request from the server and add its sub-items:

onExpandChange = (e) => {
    const items = getItemPath(data, e.level, subItemsField);
    const expandedItem = items.pop();
    const parent = items.pop();
}

We also have logged a GitHub issue for a load-a-demand demo that can be tracked and monitored here:

https://github.com/telerik/kendo-react/issues/737

I have added your request to the item in order to increase its priority.

Regards,
Filip
Progress Telerik