Native apps, Web apps communicating with same application server

Hello guys i was learning web developments and have a simple question. If i built a e-commerce web page using node.js and ejs template engine and everything works fine. The next decision is to build a native app for the same e-commerce site either android or IOS. I want the native app to also communicate with the same application server designed in node.js. Do i have to redesign the application server?

My approach or thought:

Native app will have to consume data either xml or json. So i will have to change the business logic of my endpoints. And if i do it this way, i will also have to change the way the web ui interacts with the application server and it also has to consume json or xml response using ajax call. Is my thinking or approach on the right track? But if using node.js, should i avoid the template engines?