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- Now since we recently
talked about generics

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I kind of want to expand on
that a little further by talking

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about how do you deal with
asynchronous functions,

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namely when you're working with promises.

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'Cause this is another use
case where generics come

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in really handy.

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For example, let's say I wanted to wait

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for 1,000 milliseconds

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and then I wanted to do
something with my value.

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And let's just come in here.

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I know that my value here is going to

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be a string that's being returned.

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So I could do something like value.length

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and log that out to see
how long my string is.

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You're noticing when I do that,

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I actually get an error and that's

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because it doesn't know
what the type of value is.

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It has a type of unknown

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for the value 'cause it's
like, what is this value?

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I don't know.

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The reason for that is our
promise expects a generic type to

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determine what the resolve
function here is going to be,

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'cause right now it
doesn't know what that type

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is going to be.

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Even though I've called it
with the value of high here,

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it still doesn't know what that
is going to be resolving to.

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So when you create a
promise, you can actually

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pass in here a generic
type, and in my case

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I know that this is going to be a string.

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By doing that, I've cleared

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up all of my different errors for this.

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So when I'm working

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with a function that's
dealing with a promise,

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I need to make sure I specify
the generic for that promise.

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Now I can go a step further

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by actually declaring the
return type for my function.

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'Cause if you want to return
from a asynchronous function,

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you're going to be
using promises for that,

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so you need to make sure the
return type here is a promise

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with that specific generic
type added onto it.

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Now this is automatically inferred for us

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so we don't have to add this ourselves

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but if you're dealing
with that asynchronously

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that is one thing to be aware of.

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And another really
important thing to be aware

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of is if you have a function
that's actually specified

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as an async function and you're
doing some asynchronous code

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inside of here, for
example, let's just say we

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have a really simple
fetch request going on

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and then we just return
the value from here.

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This actually also is going
to be returning a promise

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from it as well.

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So in our case, we need
to make sure we specify

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what that promise is going to be.

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So we could say like a
string, or in our case

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we could just say any,
it doesn't really matter.

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Now if we remove this
and let it just infer,

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fetch already has the
promise type enabled.

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You can see it returns a promise response.

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So down here,

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our value is going to be that
specific response object.

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So I can do like JSON, for
example, inside of here

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and that's going to work just fine.

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The important thing to note though,

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is if you have an asynchronous
function like this

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the return type always
needs to be a promise.

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So when you're consuming that

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it's always going to be
a promise return type.

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So if you need to manually type it

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you must make sure you
wrap it inside of a promise

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whatever's actually being returned.