Express.js 4 is the latest (as of May 2014) version of the most popular mature and robust Node.js framework for web apps, services and APIs. There are some breaking changes going from 3.x to 4.x, so here’s a brief migration guide:

• Replacing Unbundled Middleware in Express.js 4
• Removing Deprecated Methods from Express.js 4 Apps
• Other Express.js 4 Changes
• Express.js 4 Route Instance and Chaining It
• Further Express.js 4 Migration Reading Links

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