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
– Samir Talwar, Commented Sep 9, 2011 at 21:55
Did u figure this out? Likely a spelling error like in your description. "params?2" — Mike Mestnik
– Mike Mestnik, Commented Jun 3, 2018 at 5:34

UpTheCreek · Accepted Answer · 2013-02-04 14:36:36Z

130

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 4, 2013 at 14:36

UpTheCreek

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answered Sep 9, 2011 at 21:59

Raynos

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3 Comments

Jim Schubert Over a year ago

+1 for answering the part that the OP added in after my answer :\

Raynos Over a year ago

@JimSchubert sorry mr schubert :(

HankCa Over a year ago

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?

Jim Schubert · Accepted Answer · 2011-09-09 22:00:21Z

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 9, 2011 at 22:00

Jim Schubert

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6 Comments

user885355 Over a year ago

Thank you. My mistake was that I forgot to change the number of arguments for one of the calls.

user885355 Over a year ago

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?

Jim Schubert Over a year ago

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 for video tutorial). node-inspector is the webkit inspector (like CTRL+SHIFT+J in Chrome) which listens to node --debug.

Jim Schubert Over a year ago

@SohailSi This is a way to prevent any programmatic errors (like if someone binds a new object to both exports and module.exports). See stackoverflow.com/a/13622513/151445 for more details.

Sohail Si Over a year ago

Thank you @JimSchubert for the educational comment.

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