When comparing Sails.js vs Koa, the Slant community recommends Sails.js for most people. In the question“What are the best node.js web frameworks?” Sails.js is ranked 4th while Koa is ranked 5th. The most important reason people chose Sails.js is:
Sails.js is built with a focus on building real time communication apps such as chat or multiplayer games, so naturally it has Socket.io extremely well supported.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Transparent support for Socket.io
Sails.js is built with a focus on building real time communication apps such as chat or multiplayer games, so naturally it has Socket.io extremely well supported.
Pro MVC architecture
This could be a huge plus, if you prefer to build your apps using the Model View Controller architecture. Using Sails.js you'll find the task of separating the business logic from the user interface and keeping the interactions between them in a separate layer, extremely easy.
Pro JSON API generated for free
Exposes public JSON API for free. No additional routing to be defined. Makes it pretty easy to access data from anywhere.
Pro ORM that can be plugged into any database, or even custom web service
Sails.js uses Waterline ORM at its backend which means you can store your data in any datastore that you like; all you have to do is make a change to the Waterline adapter, this will allow you to store your data in MySQL/Redis or any other kind of database.
Pro So easy to deploy and lift
Pro Great documentation and structure
Clear documentation and easy to understand. The file structure gives you a way to understand where you can start to develop when you encounter a new Sails project
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 Poor ORM
The built-in Waterline is not well designed and is not suitable for production environments. Populating more than 1 level deep is a nightmare, there is no transaction support, new features/bug fixes are not implemented anywhere near a timely manner (the most requested feature 'deep populate' has been lingering in their github issues list for over a year and a half now).
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.