[robertknight]

To expand on the link between generators and async functions, the way that async functions were made to run in old browsers that didn't support them by tools like Babel and TypeScript was to rewrite the async function in two stages:

1. Rewrite the async function to be a generator function with a wrapper that calls `next` on the generator whenever `await`-ed Promises resolve

2. Rewrite the generator function to be a big switch statement, together with a wrapper function that drives execution.

You can play around with generators and async functions in the TypeScript playground, with TSConfig set to target ES5, to see how this works: https://www.typescriptlang.org/play?target=1#code/GYVwdgxgLg...