What is the difference between Express 3/4 and Express Framework?

Question

Going through the socket.io documentation I discovered that there is express v.3/4 and express framework. What is the difference?

Answer 1

In the context of the socket.io docs, "Express Framework" means Express 2.x.

There were a number of breaking API changes between Express 2 and Express 3. The code to use socket.io with these versions is different, which is why they are listed separately.

^{(This is so labeled because Express 2 was the only version in wide use when socket.io first came out. When v3 came out, a section was added noting the difference in API, but the original section wasn't renamed. Now, the terminology is just confusing. Issue filed.)}

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^{The following is what I posted originally, when I thought the question was asking about the difference between Express 3 and 4. Since this question is a top Google result for "difference between express 3 and 4", I'm going to leave it here.}

The difference between Express 3 and 4 is fully documented in the Express Wiki.

• Migrating from 3.x to 4.x
• New features in 4.x

The biggest change is that connect is no longer a dependency, and therefore many previously included middleware functions are no longer in the box. This means things like bodyParser are now obtained separately.

Additionally, app.router no longer exists, which means app.get etc and app.use are now processed in the exact order you add them.