how to define a file as a module in node.js

Using a non relative path to require your source files is not how node's require is intended to work! Don't try to work around this restriction by placing arbitrary code file in node_modules directory or workaround by changing the NODE_PATH environment variable.

If you want to use require without a path you should extract the required code as a node module and depend on this node module. This leads to better structured code, less complex modules, encapsulated functionality, better testability and easier code reuse.

You can include package dependencies from http or git so there is no requirement to publish node modules you use in npm. Take a look at npm dependencies for more detail.

if relative path annoy you and you want to use lib always in your application, you can use global variable like this.

var lib = require('./lib');
global.lib = lib;

you can set lib to global variable in your entry point. after then you can access just lib. but it's pollute global scope. so you have to use carefully.

placing your module in node_modules dont require you to include a path or relative path

EDIT:

if you place a file named package.json inside the module directory, Node will try to parse that file and look for and use the main attribute as a relative path for the entry point. For instance, if your

./myModuleDir/package.json

file looks something like the following, Node will try to load the file with the path

./myModuleDir/lib/myModule.js

:

{
"name" : "myModule",
"main" : "./lib/myModule.js"
}

If that folder does not contain a package definition file named package.json, the package entry point will assume the default value of index.js, and Node will look, in this case, for a file under the path ./myModuleDir/index.js.

use module.exports in the index.js file . and place it inside the node_modules folder