This is a simple contrived application to illustrate how NodeJS handles circular dependencies. It is based on (and inspired by) the blog article by Sankarsan on the same topic.
This program requires NodeJS. To run it, simply use:
npm run test
It is recommended that you use a debugger so you can observe what's happening in the code at each step.
For background, I recommend starting with Sankarsan's blog post on circular dependencies.
This example application consists of three pieces of code:
modulea.js- "Module A" - a simple CommonJS module; it has a dependency on Module B.moduleb.js- "Module B" - another simple CommonJS module; it has a dependency on Module A.app.js- the main application; it has dependencies on both Module A and Module B.
The annotations in the code and in the flowchart below describe in detail what happens when a program tries to load Modules A and B, which have dependencies on each other. The step numbers noted in the code correspond to the numbers in the diagram below.
For a more comprehensive overview of Javascript modules, I recommend the "Modules" chapter of Marijn Haverbeke's Eloquent Javascript.
For a clear explanation how exports works, I recommend this StackOverflow post.