Determine project root from a running node.js application

There are several ways to approach this, each with their own pros and cons:

require.main.filename

From http://nodejs.org/api/modules.html:

When a file is run directly from Node, require.main is set to its module. That means that you can determine whether a file has been run directly by testing require.main === module

Because module provides a filename property (normally equivalent to __filename), the entry point of the current application can be obtained by checking require.main.filename.

So if you want the base directory for your app, you can do:

var path = require('path');
var appDir = path.dirname(require.main.filename);

Pros & Cons

This will work great most of the time, but if you're running your app with a launcher like pm2 or running mocha tests, this method will fail.

global.X

Node has a a global namespace object called global — anything that you attach to this object will be available everywhere in your app. So, in your index.js (or app.js or whatever your main app file is named), you can just define a global variable:

// index.js
var path = require('path');
global.appRoot = path.resolve(__dirname);

// lib/moduleA/component1.js
require(appRoot + '/lib/moduleB/component2.js');

Pros & Cons

Works consistently but you have to rely on a global variable, which means that you can't easily reuse components/etc.

process.cwd()

This returns the current working directory. Not reliable at all, as it's entirely dependent on what directory the process was launched from:

$ cd /home/demo/
$ mkdir subdir
$ echo "console.log(process.cwd());" > subdir/demo.js
$ node subdir/demo.js
/home/demo
$ cd subdir
$ node demo.js
/home/demo/subdir

app-root-path

To address this issue, I've created a node module called app-root-path. Usage is simple:

var appRoot = require('app-root-path');
var myModule = require(appRoot + '/lib/my-module.js');

The app-root-path module uses several different techniques to determine the root path of the app, taking into account globally installed modules (for example, if your app is running in /var/www/ but the module is installed in ~/.nvm/v0.x.x/lib/node/). It won't work 100% of the time, but it's going to work in most common scenarios.

Pros & Cons

Works without configuration in most circumstances. Also provides some nice additional convenience methods (see project page). The biggest con is that it won't work if:

• You're using a launcher, like pm2
• AND, the module isn't installed inside your app's node_modules directory (for example, if you installed it globally)

You can get around this by either setting a APP_ROOT_PATH environmental variable, or by calling .setPath() on the module, but in that case, you're probably better off using the global method.

__dirname isn't a global; it's local to the current module so each file has its own local, different value.

If you want the root directory of the running process, you probably do want to use process.cwd().

If you want predictability and reliability, then you probably need to make it a requirement of your application that a certain environment variable is set. Your app looks for MY_APP_HOME (Or whatever) and if it's there, and the application exists in that directory then all is well. If it is undefined or the directory doesn't contain your application then it should exit with an error prompting the user to create the variable. It could be set as a part of an install process.

You can read environment variables in node with something like process.env.MY_ENV_VARIABLE.

1- create a file in the project root call it settings.js

2- inside this file add this code

module.exports = {
    POST_MAX_SIZE : 40 , //MB
    UPLOAD_MAX_FILE_SIZE: 40, //MB
    PROJECT_DIR : __dirname
};

3- inside node_modules create a new module name it "settings" and inside the module index.js write this code:

module.exports = require("../../settings");

4- and any time you want your project directory just use

var settings = require("settings");
settings.PROJECT_DIR; 

in this way you will have all project directories relative to this file ;)

Create a function in app.js

/*Function to get the app root folder*/

var appRootFolder = function(dir,level){
    var arr = dir.split('\\');
    arr.splice(arr.length - level,level);
    var rootFolder = arr.join('\\');
    return rootFolder;
}

// view engine setup
app.set('views', path.join(appRootFolder(__dirname,1),'views'));

All these "root dirs" mostly need to resolve some virtual path to a real pile path, so may be you should look at path.resolve?

var path= require('path');
var filePath = path.resolve('our/virtual/path.ext");

the easiest way to get the global root (assuming you use NPM to run your node.js app 'npm start', etc)

var appRoot = process.env.PWD;

If you want to cross-verify the above

Say you want to cross-check process.env.PWD with the settings of you node.js application. if you want some runtime tests to check the validity of process.env.PWD, you can cross-check it with this code (that I wrote which seems to work well). You can cross-check the name of the last folder in appRoot with the npm_package_name in your package.json file, for example:

    var path = require('path');

    var globalRoot = __dirname; //(you may have to do some substring processing if the first script you run is not in the project root, since __dirname refers to the directory that the file is in for which __dirname is called in.)

    //compare the last directory in the globalRoot path to the name of the project in your package.json file
    var folders = globalRoot.split(path.sep);
    var packageName = folders[folders.length-1];
    var pwd = process.env.PWD;
    var npmPackageName = process.env.npm_package_name;
    if(packageName !== npmPackageName){
        throw new Error('Failed check for runtime string equality between globalRoot-bottommost directory and npm_package_name.');
    }
    if(globalRoot !== pwd){
        throw new Error('Failed check for runtime string equality between globalRoot and process.env.PWD.');
    }

Maybe you can try traversing upwards from __filename until you find a package.json, and decide that's the main directory your current file belongs to.

A technique that I've found useful when using express is to add the following to app.js before any of your other routes are set

// set rootPath
app.use(function(req, res, next) {
  req.rootPath = __dirname;
  next();
});

app.use('/myroute', myRoute);

No need to use globals and you have the path of the root directory as a property of the request object.

This works if your app.js is in the root of your project which, by default, it is.