3

I've been trying to make an infinite loop in Node js, and came across this problem. I experimented a bit and came up with these three functions.

async function rc1(){
    rc1();
}
//-> stack overflow error

async function rc2(){
    await rc2();
}
//-> stack overflow error

async function a(){}
async function rc3(){
    await a();
    rc3();
}
//-> no stack overflow error

Why does this happen?

I've been reading up on the async/await tutorials, but most just post code. There are great visualizers but they don't show any examples of the await code. If there are any resources that would be great.

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  • @LãNgọcHải I think it's safe to assume OP is calling each function to test Commented Jan 9 at 3:06

1 Answer 1

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In rc2, the recursion happens synchronously. The order of operations is:

  1. call rc2
  2. wait for the promise to resolve

Even though the await keyword appears syntactically before the function call, the function call actually happens first. Since rc2 is being called synchronously, the stack overflows before any awaiting even happens.

In rc3, the recursion happens asynchronously. Order of operations:

  1. Call a()
  2. wait for the promise to resolve
  3. Call rc3

You probably already know that await makes the function return a promise. Await is actually just a "friendly" syntax to abstract away promise method chaining. You effectively get a callback function after each await. It can often be a fairly leaky abstraction, like we see here, so it's extremely helpful to learn how to use promise chaining style as well.

Any further code after await will be triggered separately by the JS engine when the promise resolves. This is done by creating a fresh stack and calling the next piece of code. So if your function awaits anything before calling itself, the code afterwards will be working with a new stack. No stack overflows.

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