Why does babel translate async/await to regenerators?

Question

All version of babel translate an await statement to a _asyncToGenerator call, it obviously has some shortcomings:

Code size grows dramatically
Requires the regeneratorRuntime library

From my understanding of the syntax I think any await should be equivalent to a Promise#then call, so the code below:

try { let user = await getUser(); console.log(user.name); } catch (error) { console.error(error); }

is just equivalent to:

let promise$of$getUser$ = getUser(); $promise$of$getUser$.then( $result$ => console.log($result$), $error$ => console.error($error$) );

In this way it is also possible to correctly map multiple await statements or even a mix of Promise#then and await statements to a Promise chain, so I must missed some cases where pure Promise#then is not suitable for await statements.

hzoo · Accepted Answer · 2016-04-09 13:51:40Z

You can use the other 2 plugins: async-to-generator and async-to-module-method.

There's also an experimental plugin called kneden which does try to do what you are suggesting (async to promise). It's still WIP and doesn't account for all cases and most likely will not be able to.

Stephen Cleary · Accepted Answer · 2016-04-09 14:40:49Z

2

I think you're overlooking loops:

for (let userId of userIds) { const user = await getUser(userId); console.log(user); }

answered Apr 9, 2016 at 14:40

Stephen Cleary

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1 Comment

otakustay Over a year ago

Thanks, after some research I find loops and conditions are possible to handle properly but is really hard, mixes of all these complexities may be the reason not to support translating await directly into Promise

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