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npm

The npm command is CLI tool that acts as a package manager for Node.js. By default it points to the npmjs.com registry, which is the default module registry.

Initializing a Package

A package is a folder with a package.json file in it.

The npm init command can be used to quickly create a package.json, it will start a CLI wizard that will ask some questions. To accept the default value for every question is to use the -y flag.

package.json some fields

  • name – the name of the package
  • version – the current version number of the package
  • description – a package description, this is used for meta analysis in package registries
  • main – the entry-point file to load when the package is loaded
  • scripts – namespaced shell scripts, these will be discussed later in this section
  • keywords – array of keywords, improves discoverability of a published package
  • author – the package author
  • contributors - is like author but accept an array
  • license – the package license.
  • repository - repository of the code

Installing Dependencies

npm install pino

Once the dependency is installed the package.json file will have the package in dependencies.

npm install

Will install all the dependencies in package.json.

The npm ls command can be used to describe the dependency tree of a package

Development Dependencies

An important characteristic of development dependencies is that only top level development dependencies are installed. The development dependencies of sub-dependencies will not be installed.

To install a package as dev dependecie:

npm install --save-dev standard

Once the dependency is installed the package.json file will have the package in devDependencies.

A --production flag can be used with npm install so that development dependencies are ignored

Scripts

The "scripts" field in package.json can be used to define aliases for shell commands that are relevant to a Node.js project.

"scripts": {
  "test": "echo \"Error: no test specified\" && exit 1",
  "lint": "standard"
},

Packages can assign a "bin" field in their package.json, which will associate a namespace with a Node program script within that package.

To execute the script use npm run:

npm run lint

There are two package scripts namespaces that have dedicated npm commands: npm test and npm start.