How to build the code for mobile app neglecting the web based components?

I have to create an application which is supported for both web, and mobile devices. So I opted for React-native, which I am new to. I build the project completely for both the mobile view, and the web view. The problem now is, how to build the code only for the mobile app neglecting the code that is applied for the web view. The build size increases for the mobile app when I build it. Any solution for this?