node.js: make a web interface for console application

I have a console application in node.js, which reads a file, (processes it) and outputs a number.

I am able to run the application using command node ex.js in the console, where ex.js is the name of my file.

I need to make a web-interface for my application, so that users are able to select the file through a File Dialog, and output is then displayed in a text box.

I need guidance on where to start from? Simply building a web-page in the same directory and calling .js functions won't work. Do I need to create a server first and then call the .js functions?