I would like to publish a npm package that contains my source as well as distribution files. My Github repository contains src
folder which contains JavaScript
Take a look at the "files" field of package.json file https://docs.npmjs.com/files/package.json#files
From the documentation:
The "files" field is an array of files to include in your project. If you name a folder in the array, then it will also include the files inside that folder. (Unless they would be ignored by another rule.)