Welcome to NodePackages

This document is focused on Node and the package.json file.

NPM ShortCuts

Task Basic Quick
Install npm install pkg npm i pkg.
Global Install npm i --global pkg npm i -g pkg.
Dependency npm i --save pkg npm i -S pkg.
Dev Dependency npm i --save-dev pkg npm i -D pkg.
Task Basic
See Scripts npm run
list dependencies npm ls --depth=0
npm Init npm init -y
npm Init npm init -f
npm test npm t


Using package.json

All your projects should include a file called package.json. To create one from scratch, go to the root of your project and issue this command:

npm init

You will be presented with a series of prompts to fill out. Just step through them one by one, leaving the ones that don't interest or confuse you blank. When you are done, there will be a file called package.json in your current directory.

To add packages to package.json, issue a command like this:

npm install require --save

This installs the package called require into a folder called node_modules. It also saves a command to install the package into package.json. To reinstall require later, just type this command:

npm install

This command processes package.json and automatically installs all the packages you saved into it. You can, of course, save information about many packages into a single package.json file.

The key point to remember is that npm install processes the contents of the file called package.json. It installs all the libraries listed in that file in a local directory called node_modules. By locally, I mean that the directory is now included in your project.

If you follow the link to package.json for BridgeSailor you will see that karma is listed in that file:

"devDependencies": {
    "requirejs": "^2.1.11",
    "karma": "^0.12.14",
    "karma-jasmine": "^0.2.0",
    "karma-requirejs": "^0.2.1",
    "karma-chrome-launcher": "^0.1.3",
    "karma-firefox-launcher": "^0.1.3"

This means that running npm install will install all the files listed above, including the karma library.

The point of npm install and package.json is that they work together to install a series of libraries, rather than asking you to type the following series of individual commands:

npm install requirejs
npm install karma
npm install karma-jasmine
npm install karma-requirejs
npm install karma-chrome-launcher
npm install karma-firefox-launcher

Typing all of the above commands is time consuming, error prone and repetitious. Therefore we use package.json, which needs to be configured correctly once, and works automatically thereafter.

Save to Package.json

To put the thing you installed in package.json use --save or --save-dev. If it is going to be used on the client side, then use --save, if it is debugging or other developer tool that is used only during development, then use --save-dev

    npm install "express" --save
    npm install "karma-script-launcher" --save-dev

Adding entries to package.json

Usually all you need to do is process package.json by typing npm install. However, you may occassionally. want to add your own dependency to package.json. Here is how to put a library called karma-script-launcher in package.json:

npm install "karma-script-launcher" --save-dev

The command shown above first installs karma-script-launcher into node_modules. It then adds an entry for it to package.json. Then next time you run npm install the karma-script-launcher package will be installed automatically because it is now included in package.json.

Consider this command:

npm install karma --save-dev

This command installs the library, and saves the library name into package.json if it is not already there.

Command Result
npm install process package.json and install all packages it references into node_modules
npm install chai install chai into node_modules
npm install chai --save install chai into node_modules and add chai to package.json
npm install chai --save-dev install chai into node_modules and add chai to package.json in a section listing packages used during development.

NPM and Express

You may have a project that depends on express. In such cases, the author of the project will probably create a file called package.json that will contain a reference to express. If this file exists, you can just type the following to install express and any other libraries that the project depends upon:

npm install

Here is the contents of a simple package.json file that installs both express and openid as well as a library called mdirp:

        "name": "OpenId04",
        "version": "0.0.1",
        "private": true,
        "scripts": {
            "start": "node ./bin/www"
        "dependencies": {
        "body-parser": "~1.13.2",
        "cookie-parser": "~1.3.5",
        "debug": "~2.2.0",
        "express": "~4.13.1",
        "jade": "~1.11.0",
        "morgan": "~1.6.1",
        "serve-favicon": "~2.3.0"      

Cannot Find Module

One useful tip:

You might see something like this:

$ npm start

> Week02-NpmBower@0.0.0 start /home/bcuser/Git/isit320-foo-2015/Week02-NpmBower
> nodemon ./bin/www

28 Sep 17:54:30 - [nodemon] 1.7.1
28 Sep 17:54:30 - [nodemon] to restart at any time, enter `rs`
28 Sep 17:54:30 - [nodemon] watching: *.*
28 Sep 17:54:30 - [nodemon] starting `node ./bin/www`
    throw err;

Error: Cannot find module 'express'

Study this error message. You are likely to see this error quite frequently. In particular, pattern Error: Cannot find module 'XXX'. Getting that error usually means we have not run npm install or we have a problem in our package.json file.

The facts are simple. We often forget to run npm install. We make mistakes in our package.json files, usually because we forgot to include --save when we installed a particular package:

They both install jquery, but only the first adds an entry to package.json.

Understanding the source of errors like those shown above is very helpful. Remember, we fix this error by running the following command:

npm install

Understand when to run that command, and what it does. In particular, understand that it processes the contents of package.json.

More on Node and Package.json

NPM related issues are specific to node, not to Linux. If you were using node on Windows or the Mac, npm behaves in a very similar fashion.

npm is the Node Package Manager. It installs libraries that are used by Node projects. Some of the libraries, such as fs (the File System package) are built into node, but most are open source projects hosted on GitHub.

Here are a few node packages (libraries) that I often install globally:

├─┬ express-generator@4.0.0
├─┬ grunt-cli@0.1.13
├─┬ jasmine-node@1.14.3
├─┬ js-beautify@1.5.1
├─┬ jshint@2.5.0
├─┬ karma-cli@0.0.4
└─┬ npm@1.4.9

These are stored here on a typical Linux system:

$ ls -l /usr/lib/node_modules/
total 28
drwxr-xr-x 5 nobody charlie 4096 Apr 21 12:24 express-generator
drwxr-xr-x 6 nobody charlie 4096 Apr 20 09:57 grunt-cli
drwxr-xr-x 9 nobody charlie 4096 Apr 21 16:02 jasmine-node
drwxr-xr-x 4 nobody charlie 4096 Apr 26 15:43 js-beautify
drwxr-xr-x 6 nobody charlie 4096 Apr 21 18:31 jshint
drwxr-xr-x 4 nobody charlie 4096 Apr 27 10:23 karma-cli
drwxr-xr-x 9 root root 4096 May 5 07:56 npm

We install these global packages by typing something like:

sudo npm install -g karma-cli

Where karma-cli is the package we want to install.

Each project also has packages that it uses. Each individual project might rely on a particular version of a package. For instance, one express project might use express 3.5.1, while another might use express 4.0.0. As a result, we don't install these packages globally. Instead, we install them inside the project we are currently using. This way, a particular project can rely on a particular version of a package. Specifically, we install them in a folder called node_modules.

Here, for instance, are the packages installed for a project called Week02Jade:

$ ls -l node_modules/
total 28
drwxrwxr-x 3 charlie charlie 4096 Apr 26 16:44 body-parser
drwxrwxr-x 5 charlie charlie 4096 Apr 26 16:44 cookie-parser
drwxrwxr-x 3 charlie charlie 4096 Apr 26 16:44 debug
drwxrwxr-x 5 charlie charlie 4096 Apr 26 16:44 express
drwxrwxr-x 5 charlie charlie 4096 Apr 26 16:44 jade
drwxrwxr-x 3 charlie charlie 4096 Apr 26 16:44 morgan
drwxrwxr-x 2 charlie charlie 4096 Apr 26 16:44 static-favicon

These packages get installed when we type npm install. This action causes npm to process the contents of package.json, and to install the packages listed there:

    $ cat package.json
      "name": "application-name",
      "version": "0.0.1",
      "private": true,
      "scripts": {
        "start": "DEBUG=my.application node ./bin/www"
      "dependencies": {
        "express": "~4.0.0",
        "static-favicon": "~1.0.0",
        "morgan": "~1.0.0",
        "cookie-parser": "~1.0.1",
        "body-parser": "~1.0.0",
        "debug": "~0.7.4",
        "jade": "~1.3.0"

Do you see that the directory listing is the same as the packages listed in package.json? The bottom line is that we need to think in terms of both global and local versions of our npm packages.

You can find all the npm packages here:

Error: Couldn't Read Dependencies

Sometimes you may also see this error:

npm install
npm ERR! install Couldn't read dependencies
npm ERR! package.json ENOENT, open '/home/charlie/package.json'

This errror occurs, needless to say, because a copy of package.json is not found. As mentioned above, there are cases when a node program does not rely on any libraries, and hence package.json does not exist. But the error above usually occurs because you are not in the proper directory. For instance, you are in your home directory, and the program you want to run is in ~/Git/JsObjects/JavaScript/Design/SimpleQueue.

To return to our main point: the primary problem that developers encounter when the see this error is simply forgetting to type npm install.

Error: Address in Use EADDRINUSE

The EADDRINUSE (Error Address In Use) message usually means that the port is in use by another program. For instance, you left an instance of a program running on the port where you want to launch your node server. Usually, fixing this is just a matter of finding the SSH or Windows command prompt where the server is running, and pressing Ctrl-C to stop the server:

C:\Git\P282\CanvasGrid>node server.js
  Listening on port :30026
^C   <== Here I press Ctrl-C

An important variation on this error can occur if you are running upstart. Details about that variant of the EEADDRINUSE error are discussed below.