How to share code between node.js apps?

The npm documentation recommends using npm-link to create your own Node.js packages locally, and then making them available to other Node.js applications. It's a simple four-step process.

A typical procedure would be to first create a package with the following structure:

  hello
  | index.js
  | package.json

A typical implementation of these files would be:

index.js

  exports.world = function() {
     return('Hello World');
  }

package.json

  {
    "name": "hello",
    "version": "0.0.1",
    "private": true,
    "main": "index.js",
    "dependencies": {
    },
    "engines": {
    "node": "v0.6.x"
    }
  }

"private:true" ensures that npm will refuse to publish the package. This is a way to prevent accidental publication of private packages.

Next, navigate to the root of your Node.js package folder and run npm link to link the package globally so it can be used in other applications.

To use this package in another application, e.g., "hello-world", with the following directory structure:

 hello-world
 | app.js

Navigate to the hello-world folder and run:

 npm link hello

Now you can use it like any other npm package like so:

app.js

  var http = require('http');
  var hello = require('hello');

  var server = http.createServer(function(req, res) {
     res.writeHead(200);
     res.end(hello.world());
  });
  server.listen(8080);

I've got this working by having node_modules folders at different levels - node then automatically traverses upwards until it finds the module.

Note you don't have to publish to npm to have a module inside of node_modules - just use:

"private": true

Inside each of your private package.json files - for your project I would have the following:

app1
 server.js
 node_modules
  (public modules from npm needed for app1)
  (private modules locally needed for app1)

app2
 server.js
 node_modules
  (public modules from npm needed for app2)
  (private modules locally needed for app2)

node_modules
  (public modules from npm needed for app1 & app2)
  (private modules locally for app1 & app2)

The point is node.js has a mechanism for dealing with this already and it's awesome. Just combine it with the 'private not on NPM' trick and you are good to go.

In short a:

require('somemodule')

From app A or B would cascade upwards until it found the module - regardless if it lived lower down or higher up. Indeed - this lets you hot-swap the location without changing any of the require(...) statements.

node.js module documentation

Just use the correct path in your require call

For example in server.js that would be:

var moduleName = require('../shared_lib/moduleName/module.js');

Its Important to know that as soon as your path is prefixed with '/', '../', or './' the path is relative to the calling file.

For further information about nodes module loading visit: http://nodejs.org/docs/latest/api/modules.html

Yes, you can reference shared_lib from app1, but then you run into a problem if you want to package and deploy app1 to some other environment, such as a web server on AWS.

In this case, you're better off installing your modules in shared_lib to app1 and app2 using "npm install shared_lib/module". It will also install all the dependencies of the shared_lib modules in app1 and app2 and deal with conflicts/duplicates.

See this: How to install a private NPM module without my own registry?

If you check out the node.js docs, you'll see that Node.js understands the package.json file format as well, at least cursorily.

Basically, if you have a directory named foo, and in that directory is a package.json file with the key-value pair: "main": "myCode.js", then if you try to require("foo") and it finds this directory with a package.json file inside, it will then use foo/myCode.js for the foo module.

So, with your directory structure, if each shared lib has it's own directory with such a simple package.json file inside, then your apps can get the shared libs by:

var lib1 = require('../shared_lib/lib1');
var lib2 = require('../shared_lib/lib2');

And that should work for both of these apps.