In this case, Koa uses generators and promises together to emulate the behavior of async/await style concurrency. You can see how Babel 5.x transforms ES7 async

In this case, Koa uses generators and promises together to emulate the behavior of async/await style concurrency. You can see how Babel 5.x transforms ES7 async/await into generators and promises at https://github.com/babel/babel/blob/v5.8.34/packages/babel/src/transformation/templates/helper-async-to-generator.js https://github.com/babel/babel/blob/v5.8.34/packages/babel/s...