weird behavior of module require in nodejs

Question

It's hard to explain so I will reproduce the code.

I have two class files.

Business.js

const Street = require("./Street");

module.exports = class Business {};

Street.js

const Business = require("./Business");

module.exports = class Street {
  constructor() {
    console.log(Business);
  }
};

and index.js file

const Street = require("./Street");

const street = new Street();

when I run index.js (node ./index.js), it log [Function: Business] as expect,

but when I require Business.js in index.js file like below, log message change, it log empty object {}.

index.js

const Business = require("./Business");
const Street = require("./Street");

const street = new Street();

I don't understand why require Business in index.js effect log message in Street.js file.

try it out codesandbox.

Answer 1

Seems like there is a circular dependency. Ideally a module should not depend on a module that depend on that module.

Since your Business.js module depend on Street.js module and Street.js module depend on Business.js module (which is called a circular dependency) you are getting this "weird behavior".

Any restructure that avoid circular dependency will be okay, like moving both classes to the same file (just a suggestion, you may want to use another way as your use case and coding practices).

class Street {
  constructor() {
    console.log(Business);
  }
}

class Business {}

module.exports = {
  Street,
  Business
}; 

try it out codesandbox.