/!\ I'm afraid this approach is a dead end, for various reasons. Check out npm-run instead. /!\

npm-run-shell

Runs a shell in the npm run-script environment.

It adds the binaries of local npm packages in the command path, and optionally passes the npm_* environment variables to the child shell.

Installation:

in the target package:

$ npm install npm-run-script

Pass -D to npm install if you want to save it to the "devDependencies".

Then add this to the in the "scripts" sections of your package.json:

{
    "scripts":{
        "shell": "npm-run-shell"
    }
}

Usage:

    npm run shell [npmenv]

You'll get a shell

Without the npmenv option, you get a new shell prompt and the binaries exported by the package dependencies will be runnable.

Passing npmenv, you'll get the same shell, but with the environment variables set by NPM also available.

Known issues

• At this point, the shell is non-interactive in Windows, and it exits immediately (at least if your shell is cmd.exe).
• If your startup scripts (.bashrc and friends) alter the $PATH variable, you may end up with local NPM binaries shadowed by the ones of the system, notably global NPM ones. TODO: figure out how to give them more priority, possibly by tweaking the startup files using a custom environment variable to trigger a 'rotate the paths' code path.
• the nested shell starts at the root of the current project, because npm run sets it as current directory. I couldn't find a workaround that doesn't rely on a global script. npm-run-shell runs from within the run-script environment and the information is lost AFAICT.