Load the gltf or 3dtile data folder into cesium by dragging and dropping

Ask everyone; I want to load the gltf or 3dtile data folder (or zip) into cesium by dragging and dropping, similar to this(https://gltf-viewer.donmccurdy.com/). What should I do? At the same time, I found that the dragged file is not uploaded directly to the server, but loaded directly on the browser side, is that so? Very much looking forward to help, thanks.