npm gets its config settings from the command line, environment variables, and npmrc files.
The npm config command can be used to update and edit the contents of the user and global npmrc files.
For a list of available configuration options, see npm help 7 config.
The four relevant files are:
All npm config files are an ini-formatted list of key = value parameters. Environment variables can be replaced using ${VARIABLE_NAME}. For example:
prefix = ${HOME}/.npm-packages
Each of these files is loaded, and config options are resolved in priority order. For example, a setting in the userconfig file would override the setting in the globalconfig file.
Array values are specified by adding "[]" after the key name. For example:
key[] = "first value" key[] = "second value"
NOTE: Because local (per-project or per-user) .npmrc files can contain sensitive credentials, they must be readable and writable only by your user account (i.e. must have a mode of 0600), otherwise they will be ignored by npm!
Lines in .npmrc files are interpreted as comments when they begin with a ; or # character. .npmrc files are parsed by npm/ini https://github.com/npm/ini, which specifies this comment syntax.
For example:
# last modified: 01 Jan 2016 ; Set a new registry for a scoped package @myscope:registry=https://mycustomregistry.example.org
When working locally in a project, a .npmrc file in the root of the project (ie, a sibling of node_modules and package.json) will set config values specific to this project.
Note that this only applies to the root of the project that you're running npm in. It has no effect when your module is published. For example, you can't publish a module that forces itself to install globally, or in a different location.
Additionally, this file is not read in global mode, such as when running npm install -g.
$HOME/.npmrc (or the userconfig param, if set in the environment or on the command line)
$PREFIX/etc/npmrc (or the globalconfig param, if set above): This file is an ini-file formatted list of key = value parameters. Environment variables can be replaced as above.
path/to/npm/itself/npmrc
This is an unchangeable "builtin" configuration file that npm keeps consistent across updates. Set fields in here using the ./configure script that comes with npm. This is primarily for distribution maintainers to override default configs in a standard and consistent manner.