Using package.json

All Node modules must include a package.json file in their root directory. package.json is a simple JSON text file that defines a module, including dependencies. The package.json file can contain a number of different directives to tell the Node Package Manager how to handle the module.

The following is an example of a package.json file with a name, version, description, and dependencies:

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{
    "name": "my_module",
    "version": "0.1.0",
    "description": "a simple node.js module",
    "dependencies" : {
        "express"   :  "latest"
    }
}

The only required directives in the package.json file are name and version; the rest depend on what you would like to include. Table 3.2 describes the most common directives.

Table 3.2 Directives used in the package.json file

A great way to use package.json files is to automatically download and install the dependencies for your Node.js app. All you need to do is create a package.json file in the root of your project code and add the necessary dependencies to it. For example, the following package.json file requires the express module as a dependency:

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{
    "name": "my_module",
    "version": "0.1.0",
    "dependencies" : {
        "express"   :  "latest"
    }
}

Then you run the following command from the root of your package, and the express module is automatically installed:

npm install

Notice that no module is specified in the command npm install. That is because npm looks for a package.json file by default. Later, as you need additional modules, all you need to do is add those to the dependencies directive and then run npm install again.