KPC
Kevin Powell - Community•6d ago
Faker

Other external function being executed while await waits for promise in "inner" function

Hello, I have a question when it comes to JS returning promises, more specifically with async and await. Consider these code: 
async function fetchProducts() {

  ...
  const result = await somethingThatReturnAPromise();
}

function checkNumberOfProducts() {...}

function start() {
  fetchProducts()
  checkNumberOfProducts()
}
async function fetchProducts() {

  ...
  const result = await somethingThatReturnAPromise();
}

function checkNumberOfProducts() {...}

function start() {
  fetchProducts()
  checkNumberOfProducts()
}
start is a function that "runs" our app. My question is when we await inside our fetchProducts() that is we are waiting for the promise to be resolved, inside start(), does execution shifts to checkNumberOfProduct() even though fetchProducts() hasn't been completed? If so, can someone explain why pls.
4 Replies
Ganesh
Ganesh•6d ago
This is because of scope. Your fetchProducts function is awaiting somthingThatReturnsAPromise But that's only within the scope of fetchProducts Your start function doesn't know anything about what's going on inside the fetchProducts function it just sees that it needs to execute two functions. You will need to await the fetchProducts inside start function too. All async functions return a promise so they can also be awaited
Faker
FakerOP•6d ago
oh ok I see yep make sense, ty !
13eck
13eck•5d ago
You can think of async and being "contagious" or "insidious" (depending on how you view that keyword 😉 ). Anything that touches an async function must be declared async as well otherwise it won't be able to await the result! And if you miss one await in the chain…you're screwed 🤣 For this reason I suggest not nesting async code if you can avoid it. One, maybe two calls deep is the max I recommend, anything else might be a code smell (as it's trying to do too much). Break those deeply-nested async calls into smaller functions to flatten the nesting.
Faker
FakerOP•5d ago
Yepp noted, thanks !

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