How do I resolve "Cannot find module" error using Node.js?

Using npm install installs the module into the current directory only (in a subdirectory called node_modules). Is app.js located under home/dave/src/server/? If not and you want to use the module from any directory, you need to install it globally using npm install -g. I usually install most packages locally so that they get checked in along with my project code. Update (8/2019): Nowadays you can use package-lock.json file, which is automatically generated when npm modifies your node_modules directory. Therefore you can leave out checking in packages, because the package-lock.json tracks the exact versions of your node_modules, you're currently using. To install packages from package-lock.json instead of package.json use the command npm ci. Update (3/2016): I've received a lot of flak for my response, specifically that I check in the packages that my code depends on. A few days ago, somebody unpublished all of their packages (https://kodfabrik.com/journal/i-ve-just-liberated-my-modules) (archived on Wayback Machine) which broke React, Babel, and just about everything else. Hopefully it's clear now that if you have production code, you can't rely on NPM actually maintaining your dependencies for you.