Understanding module.export to pass a parameter

Question

I have been trying to understand, module.export how to pass a parameter with it. Now I have made a demo server for testing it.

File - index.js

var express = require('express');
var check = require('./file');
var app = express();

app.get('/',check.fun1("calling"),(req,res)=>{
    res.send('here i am');
})

app.listen(3000,()=>{
    console.log("Server is up");
})

With a middleware check,

module.exports = fun1 = name => {
    return function(req, res, next) {
      console.log(name + " from fun1");
      next();
    };
  };

  module.exports = fun2 = name2 => {
    return function(req, res, next) {
      console.log(name + " from fun1");
      next();
    };
  };

Now this is not working, but when I change it in, its start to work

fun1 = name => {
  return function(req, res, next) {
    console.log(name + " from fun1");
    next();
  };
};

fun2 = name2 => {
  return function(req, res, next) {
    console.log(name + " from fun1");
    next();
  };
};

module.exports = {
  fun1,
  fun2
};

Now, this might look like a stupid question, that if it's working then why I am asking but, what change should I make, in index.js file so that my first type of module.export starts working. It's just all out of sheer curiosity

Thanks

What do you expect module.exports = fun1 = name => {...} to do? What's the purpose of fun1 here? If you want to export two functions from your module, then you write exports.fun1 = name => {...} and exports.fun2 = name2 => {...}. You only overwrite module.exports if you want to export a single value. Not sure how the title of the questions relates to your issue. — Felix Kling
– Felix Kling, Commented Sep 8, 2019 at 10:05
Ok, I get now, exports.mdoule is basically an obj in the module, if I export it twice it gets overwritten, hmmm, making sense. But exports is directly converted to module.export hmmm.. thankx — Alpit Anand
– Alpit Anand, Commented Sep 8, 2019 at 10:24
exports is simply a variable in scope of a module and initially references the same value as module.exports. — Felix Kling
– Felix Kling, Commented Sep 8, 2019 at 13:07

slebetman · Accepted Answer · 2019-09-08 10:36:39Z

A lot of things in node.js are simply design patterns. Node.js introduced exactly zero extensions to javascript when it was originally published (and this includes its module system). Even today, node.js has zero syntax extensions. Node.js is just javascript with additional libraries and a special runtime environment (where all modules are evaluated inside an IIFE)

Having said that, module.exports is not syntax. It is simply an ordinary variable in javascript. Specifically, the variable module is an object and node's module system will check this module variable to see if it has a property named exports. If module has an exports property then its value is taken to be the exported module.

Since module is just an ordinary variable it follows normal variable behaviour. If you reassign a variable its value will change. For example:

var x = 0;
console.log(x); // prints 0;
x = 100;
console.log(x); // prints 100, not 0 and 100

Therefore, the same is true for module.exports:

module.exports = 'hello';
console.log(module.exports); // prints 'hello'
module.exports = 'world';
console.log(module.exports); // prints 'world', not 'hello world'

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