The example extension demonstrates how to build tree editors in Eclipse Theia, which show the content of JSON files.
In the running application, open the menu "Tree Editor"=>"New Example File" (a workspace must be opened).
The created .tree file will automatically be opened with the example tree editor.
The left side of the editor shows the hierarchy of the JSON data allowing you to create new children and delete nodes.
The right site shows the properties of a selected node and allows the modification of the same.