CODEWITHSUNDEEP
javascriptnode.jsexpresspouchdb
Christer Olsen
Christer Olsen

Reputation: 13

Difference between require('module')() and const mod = require('module') mod() in node/express

I have two files: server.js and db.js

server.js looks as such:

...
const app = express();

app.use('/db', db());

app.listen(3000, () => {
  console.log('Server started on port 3000')
});
...

and db.js as such:

...
function init() {
  const db = require('express-pouchdb')(PouchDB, {
    mode: 'minimumForPouchDB'
  });

  return db;
}
...

This works just fine, and I am able to reach the pouchdb http-api from my frontend. But before, I had const PouchDBExpress = require('pouchdb-express'); in the top of db.js, and the first line in init() looked like this; const db = PouchDBExpress(PouchDB, {. This gave an error in one of the internal files in pouchdb saying cannot set property query on req which only has getters (paraphrasing).

So this made me copy the exaples from pouchdb-servers GitHub examples which requires and invokes pouched-express directly, and everthing worked fine. Is there an explanation for this? I'm glad it works now, but I'm sort of confused as to what could cause this.

Upvotes: 0

Views: 227

Answers (2)

Harshit Sinha
Harshit Sinha

Reputation: 31

In require('module')(), you don't retain a reference of the module imported.

While in const mod = require('module'); mod(), you retain a reference and can use the same reference later in your code.

This problem might be due to some other reason like -

  1. Are you using a some another global instance of the db, and your code works in the given case as you are making a local instance
  2. Some other code dependent scenario.

Please provide more details for the same

Upvotes: 0

jfriend00
jfriend00

Reputation: 707696

The only difference between:

require('module')()

and

const mod = require('module');
mod();

is that in the second case, you retain a reference to the module exports object (perhaps for other uses) whereas in the first one you do not.

Both cases load the module and then call the exported object as a function. But, if the module export has other properties or other methods that you need access to then, obviously, you need to retain a reference to it as in the second option.

For us to comment in more detail about the code scenario that you said did not work, you will have to show us that exact code scenario. Describing what is different in words rather than showing the actual code makes it too hard to follow and impossible to spot anything else you may have inadvertently done wrong to cause your problem.

Upvotes: 3

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