Are there any downsides to using Javascript and Typescript together in a React Project? [closed]

I have a big project and it has been in development for about 2 years. More than 700 pages have been written using javascript so far and all components have been written in javascript. I recently learned about typescript's advantages over javascript and found it to be more comprehensive for large projects. New pages and new features will be added to this project. In the next process, should I write new pages with typescript or should the whole project go on a single structure? Is there a downside to having both typescript and javascript in a project? Looking forward to your suggestions on this topic.