Traditionally, most browser-based text editors have been using <input type="file"> to allow users to pick/open files and <a download> to allow users to download/save files. They also could not access the user's file system and give the option to save the edited files in place or reload the file content from disk after they file has been modified by another application, so they couldn't provide the same user experience as the native text editors.
This changed with the introduction of the File System Access API, now implemented in many desktop browsers. With this API, it is now possible to build browser-based text editors that behave like native text editors. This tool is an example of such an editor.