IMPORTANT! As Patrick noted, Webpack can handle this now, so you don't need to install it separately. It is moved as a direct dependency on Webpack.
OLD ANSWER
node-libs-browser is a peer-to-peer dependency of Webpack. As indicated on the package page, it provides specific Node libraries for use by the browser. Obviously modules like fs are not available, but you can still use quite a lot.
It is recommended that peer dependency versions be maintained, as is their own. In fact, this will be the default starting with npm 3. They are currently installed automatically. Therefore, it would be nice if they explicitly pointed to devDependencies , even if this might seem like some additional work at the moment.
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