Thank you for clearing that one out for me, Antonio.
First of all, follow these instructions Build a Pluggable Web Widget: Part 1 - Studio Pro 9 How-to's | Mendix Documentation and Build a Pluggable Web Widget: Part 2 (Advanced) - Studio Pro 9 How-to's | Mendix Documentation in order to get acquainted with the issue.
Your class needs a con structor, so if I understand correctly: your .tsx file has a class, preferably you extend this class with Component<YourProps>. Your props (.d.ts-file) export an interface with the properties you desire.
Hope this helps.