I'm not quite sure I entirely follow the question, but I'm happy to try to answer (and also chat more directly over in the Reactiflux Discord where I usually hang out, if that's easier - <a href="https://www.reactiflux.com" rel="nofollow">https://www.reactiflux.com</a> , can ping me @acemarke in a channel like #general-tech ).<p>I'm sort of wondering if part of the confusion is seeing the name `node_modules`.<p>The `node_modules` folder _was_ originally created as the place for the NPM package manager to install packages that were, yes, _only_ for use inside the Node JS runtime.<p>_However_... in today's development world, _all_ libraries your app depends on, both for building the project _and_ for runtime behavior, get installed into the `node_modules` folder of a project. That includes libraries that _only_ run under Node, libraries that _only_ run in a browser, and libraries that can be used on either side.<p>So, think of the `node_modules` folder not as strictly "a place to install packages that only run under Node", but rather "a place to install _all_ packages used in this JS project, of any kind".<p>As an example: the React library is normally used for client-side rendering. If I do `npm install react`, it will get extracted to `./node_modules/react/`. I then do `import React from "react"` in my client-side only code, and a bundler like Webpack will end up adding the React library code to my final generated browser JS bundle when I run the build step.<p>On the other hand, you can _also_ use React on the server side as well, such as pre-generating HTML while handling an HTTP request, and you would again do `import React from "react"` in server-side code too.<p>At the same time, the Lodash utility lib (which is generic JS code that can be used anywhere) and the Webpack bundler (which is a build/dev-time only tool) would _also_ all get installed to their respective folders in `node_modules`, along with any other libraries they themselves depend on.<p>You might want to read through my "How Web Apps Work" series to see how some of these different pieces come together:<p><a href="https://blog.isquaredsoftware.com/series/how-web-apps-work" rel="nofollow">https://blog.isquaredsoftware.com/series/how-web-apps-work</a>