如何在异步 function 之外访问 promise 值

Question

I'm trying to understand how promises, callbacks etc work in node.js, particularly in the case of accessing the value outside of the function. I've spent time going through the answers here How do I return the response from an asynchronous call? and here call Stripe API with await but every variation I try I always end up with 'subscription' outside the function as undefined.

Thanks

let subscription;
async function getSub(){
    subscription = await stripe.subscriptions.retrieve('sub_HurxwcQoCIH7jv');
    // code here only executes _after_ the request is done?
    return subscription
}
getSub()
console.log("subscription: ", subscription) // subscription undefined??

Answer 1

There are 2 ways you can get a response

getSub()
.then(subscription => {
    console.log("subscription: ", subscription);
});

Or

const funcA = async() {
    const subscription  = await getSub();
    console.log("subscription: ", subscription);
}
funcA();

Answer 2

The code written after the async function is executes AFTER the sync function but getting done BEFORE the async function so it will be undefined as set in the first line let subscription // undefined

Lets cut it into pieces and number the chronology of happens:

1. let subscription;
2. async function getSub(){
    5. subscription = await stripe.subscriptions.retrieve('sub_HurxwcQoCIH7jv');
    // code here only executes _after_ the request is done?
    6. return subscription
}
3. getSub()
4. console.log("subscription: ", subscription) // subscription undefined??

So as you can see, the console log will happen BEFORE the assignment because 2. takes longer than 3. and 4. because of 5. in it.

You should do something like this:

(async () => {
  const sub = await stripe.subscriptions.retrieve('sub_HurxwcQoCIH7jv')
  console.log(sub) //
})()

You can also name the function:

const functionWithSomeName = async () => {
  const sub = await ...CODE HERE...
  console.log(sub)
}

functionWithSomeName()