There are 2 ways that you can do to export data out from the datagrid.

1. You can format the data and write it to TextArea where users can use the mouse to highlight and use Ctrl+C to copy it.
2. You can send the formatted data back to server and the server-side script like servlet will return the data with the right MIME-TYPE. For this to work, you need to use FileReference API. (detailed)