Node.js "require" function and parameters

Question

When I do:

lib = require('lib.js')(app)

is app actually geting passed in?

in lib.js:

exports = module.exports = function(app){}

Seems like no, since when I try to do more than just (app) and instead do:

lib = require('lib.js')(app, param2)

And:

exports = module.exports = function(app, param2){}

I don't get params2.

I've tried to debug by doing:

params = {}
params.app = app
params.param2 = "test"

lib = require("lib.js")(params)

but in lib.js when I try to JSON.stringify I get this error:

"DEBUG: TypeError: Converting circular structure to JSON"

What are the variables you're passing in? Are they declared and defined? — Samir Talwar, Sep 09 '11 at 21:55
Did u figure this out? Likely a spelling error like in your description. "params?2" — Mike Mestnik, Jun 03 '18 at 05:34

score 129 · Answer 1 · edited Feb 04 '13 at 14:36

129

When you call lib = require("lib.js")(params)

You're actually calling lib.js with one parameter containing two properties name app and param2

You either want

// somefile
require("lib.js")(params);
// lib.js
module.exports = function(options) {
  var app = options.app;
  var param2 = options.param2;
};

or

// somefile
require("lib.js")(app, param2)
// lib.js
module.exports = function(app, param2) { }

edited Feb 04 '13 at 14:36

UpTheCreek

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answered Sep 09 '11 at 21:59

Raynos

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+1 for answering the part that the OP added in after my answer :\ – Joseph Yaduvanshi Sep 09 '11 at 22:06
@JimSchubert sorry mr schubert :( – Raynos Sep 09 '11 at 22:29
And then to have actual exports from my nodejs code I have `module.exports = function(options) { ....; return { fn1, fn2 }};` This works though is there a better way? – HankCa Aug 22 '18 at 05:46

score 21 · Answer 2 · answered Sep 09 '11 at 22:00

21

You may have an undefined value that you're trying to pass in.

Take for instance, requires.js:

module.exports = exports = function() {
   console.log('arguments: %j\n', arguments);
};

When you call it correctly, it works:

node
> var requires = require('./requires')(0,1,2,3,4,5);
arguments: {"0":0,"1":1,"2":2,"3":3,"4":4,"5":5}

If you have a syntax error, it fails:

> var requires = require('./requires')(0,);
... var requires = require('./requires')(0,2);
...

If you have an undefined object, it doesn't work:

> var requires = require('./requires')(0, undefined);
arguments: {"0":0}

So, I'd first check to see that your object is defined properly (and spelled properly when you pass it in), then check that you don't have syntax errors.

answered Sep 09 '11 at 22:00

Joseph Yaduvanshi

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1

Thank you. My mistake was that I forgot to change the number of arguments for one of the calls. – user885355 Sep 09 '11 at 22:22
Now I understand how this works a bit better. My remaining question is now about the JSON error. Do most people just debug through the browser? – user885355 Sep 09 '11 at 22:41
As far as I know, most people use `util.inspect` to inspect objects (this is done internally with `console.log`). You can also use node-inspector (see [article](http://howtonode.org/debugging-with-node-inspector) for video tutorial). node-inspector is the webkit inspector (like CTRL+SHIFT+J in Chrome) which listens to `node --debug`. – Joseph Yaduvanshi Sep 09 '11 at 23:37
Why did you also assign a variable called `exports` in line `module.exports = exports =...` ? – Sohail Si Feb 25 '19 at 19:28
1

@SohailSi This is a way to prevent any programmatic errors (like if someone binds a new object to both `exports` and `module.exports`). See https://stackoverflow.com/a/13622513/151445 for more details. – Joseph Yaduvanshi Feb 26 '19 at 20:14
1

Thank you @JimSchubert for the educational comment. – Sohail Si Feb 28 '19 at 10:44

Node.js "require" function and parameters

2 Answers2

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