https://docs.npmjs.com/cli/link
Package linking is a two-step process.
First, npm link in a package folder will create a globally-installed symbolic link from prefix/package-name to the current folder (see npm-config for the value of prefix).
Next, in some other location, npm link package-name will create a symlink from the local node_modules folder to the global symlink.
Note that package-name is taken from package.json, not from directory name.
原文：http://www.cnblogs.com/skating/p/6116776.html