Specifying Dependencies

Let's say you have two packages demo-package and demoforsantanu. The package demoforsantanu depends on the package demo-package. Here is the sample code below -

// @ssantanuberaa/demo-package
exports.printMessage = function(){
	console.log("Hello World");
};

// demoforsantanu
import demo = require("@ssantanuberaa/demo-package");
exports.printMsg = function() {
  return demo.printMessage();
}

To specify the packages your project depends on, you must list them as "dependencies" or "devDependencies" in your package’s package.json file. When you (or another user) run npm install packageName, npm will download dependencies and devDependencies that are listed in package.json that meet the semantic version requirements listed for each.

• dependencies : Packages required by your application in production.
• devDependencies : Packages that are only needed for local development and testing.

You can add dependencies to a package.json file from the command line or by manually editing the package.json file.

Using CLI

To add dependencies and devDependencies to a package.json file from the command line, you can install them in the root directory of your package using the --save-prod flag for dependencies (the default behavior of npm install) or the --save-dev flag for devDependencies.

To add an entry to the "dependencies" attribute of a package.json file, on the command line, run the following command:

npm install packageName [--save-prod]

To add an entry to the "devDependencies" attribute of a package.json file, on the command line, run the following command:

npm install packageName --save-dev

After installing dependencies, the package.json file will be automatically updated. The entry will be added in the dependencies object.

Using Text Editor

To add dependencies to a package.json file, in a text editor, add an attribute called "dependencies" that references the name and semantic version of each dependency:

{
  "name": "my_package",
  "version": "1.0.0",
  "dependencies": {
    "my_dep": "^1.0.0",
    "another_dep": "~2.2.0"
  }
}

To add devDependencies to a package.json file, in a text editor, add an attribute called "devDependencies" that references the name and semantic version of each devDependency:

"name": "my_package",
"version": "1.0.0",
"dependencies": {
  "my_dep": "^1.0.0",
  "another_dep": "~2.2.0"
},
"devDependencies" : {
  "my_test_framework": "^3.1.0".
  "another_dev_dep": "1.0.0 - 1.2.0"
}

After adding the dependencies run npm install to update your dependencies. It will install the dependencies in the node_modules directory.

So in our case we need to update the package.json file of demoforsantanu package as this package depends on another package. So the package.json file will look like this -

{
	"name": "demoforsantanu",
	"version": "1.1.0",
	"description": "",
	"main": "index.js",
	"scripts": {
		"test": "echo \"Error: no test specified\" && exit 1"
	},
	"keywords": [],
	"author": "",
	"license": "ISC",
	"dependencies": {
		"@ssantanuberaa/demo-package": "^1.0.0"
	}
}

Now when someone install your package demoforsantanu, the NPM will also install all the dependencies that are mentioned in the package.json file of demoforsantanu.

Also, if other application (say, demo) uses your package demoforsantanu, that application's package.json file will look like the following -

{
  "name": "demo",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "demoforsantanu": "^1.1.0"
  }
}

As you can see, the package.json file of demo package has also dependencies demoforsantanu as this application depends on demoforsantanu and demoforsantanu depends on demo-package.