// the old way

const cp = require('child_process');
const k = cp.spawn('npm', ['install','lodash']);
k.stdout.on('data', yourHandlerHere);

// the more generic way

const cp = require('child_process');
const k = cp.spawn('bash');
k.stdout.on('data', yourHandlerHere);
k.stdin.write('npm install lodash');
k.stdin.end('\n');