If you're looking at some JavaScript code you got from elsewhere, probably Node.js packages, you'll notice each has a file called 'package.json'. This will be in the module's base or root directory. This file is a sort of manifest file for the module, most likely an npm module/package. Any package listed at npmjs.com needs a package.json, and the absolute minimum the file should contain is the package's name and version. The name and version make up a unique key for the package within npmjs.
The file usually contains much more than name and version. You can guess by the...