When comparing Revel vs Koa, the Slant community recommends Koa for most people. In the question“What are the best backend web frameworks?” Koa is ranked 33rd while Revel is ranked 38th. The most important reason people chose Koa is:
Using generators (a bleeding edge feature, even for Node.js) would clean up your code from the mess caused by all those callbacks; making your code more manageable.
Specs
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Pros
Pro Comes bundled with a code reload tool
Revel comes bundled with a code reload tool which rebuilds the project on every file change. This code reload tool is also used to run, build and deploy the Revel application that you are building.
Pro Good examples easy to understand with simple emulated MVC behavior
Pro No need to find and install external libraries
Revel is a "batteries included" web framework, which means that a lot of features already come out of the box. This way you don't have to spend time and find third-party libraries to integrate to the framework for most of the tasks you need to complete.
Pro Easy to learn for fast development
Pro Generator support from ground up
Using generators (a bleeding edge feature, even for Node.js) would clean up your code from the mess caused by all those callbacks; making your code more manageable.
Pro Extremely lightweight
Koa is very lightweight with just 550 lines of code.
Pro async/await keywords are supported and has transcended beyond generator functions
Generators functions are of course a huge plus, but at the time Koa team has transcended generations functions and shifted towards async/await style programming. It has made the Koa best framework available in the market.
Pro Development team has a proven track record
Koa is developed by the team behind a widely used node.js framework (express.js).
Pro Built for ES6
Cons
Con Non-idiomatic code
Con Outdated
The world has moved past its MVC obsession. It's not the way the web works anymore. The good thing about go is that it's trivial to write a server applications (literally takes minutes). relying on a bloated, archaic framework is missing the point
Con Dead
Thankfully, this abomination is no longer being developed
Con No official support for mongo
Revel does not come with any support for MongoDB, you can integrate third-party libraries but they have been reported to crash under heavy load.
Con Community is relatively small
Con Not compatible with express style middleware
Koa uses generators which are not compatible with any other type of Node.js framework middleware.