npm - install dependencies for a package in a different folder?

I have the following directory structure:

/some_project
    source.js
    package.json

I would like to install the dependencies for some_project. I know I could cd into some_project and then run npm install

But I was wondering if it's possible without changing the directory ? Something like

npm install some_project/package.json 

You can use the npm install <folder> variant with the --prefix option. In your scenario the folder and prefix will be the same:

npm --prefix ./some_project install ./some_project

No, npm will always install in the current directory or, with -g, in the system wide node_modules. You can kind of accomplish this with a subshell though, which won't affect your current directory:

(cd some_project && npm install)

The parentheses makes it run in a subshell.

I don't think it's possible. It always installs in the local directory, or globally if the -g option is specified.
Sorry bro...maybe you can request it as a feature.