Manish, you'll notice you have some downvotes on this question. I'm not entirely sure what your question is. In the future, please use a more descriptive title, and add more detail to the body of your question. Please spend some time to make sure your sentences are complete.

I think you're asking if you can add a reference to a javascript file into the mendix index.html file, and you can. It's in the theme folder in your project directory.

Based on the questions you've been asking recently, I would highly recommend you work through the Mendix Intro training, if you haven't already: here

Then, I would recommend you review the reference guides available: here as well as the how-to guides: here

We also have webinars that you can watch on specific topics, and recently one on styling that my interest you. These are all available: here

Good luck!