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Now we're almost done,

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but there is one last feature

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which you must know as a developer when working

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with async code and Promises, and that's important.

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This concept now only applies to Promises.

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Promises already allow us

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to write code a little bit more structured

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than having multiple callback functions

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that potentially might be nested into each other.

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Still, we have to write these extra Then methods.

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And now let's assume we have a function.

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Like this readFile function here

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that performs only one long taking asynchronous operation,

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or maybe multiple operations stats depend on each other,

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but not multiple operations that should be started

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at the same point of time.

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If that's the case, if we only have one operation,

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or if we have dependent operations,

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then we still might have some async code

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because maybe the package,

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we're using at the operation we're performing,

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doesn't give us async version of the method

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as readFile did before.

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There we always had readFileSync as an alternative,

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but that's pretty much an exception.

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Most packages don't give us such a sync alternative

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when doing some async work,

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and therefore we might be stuck with using a promise

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or a callback function.

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Even though we might know that the code,

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after reading the file,

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should only execute once that's done.

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So we don't want to execute it earlier.

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Well, of course we can then move that code here

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into this Then block,

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but still we have to write all that extra Then logic,

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and we have to deal with those callback functions.

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In scenarios like this, you can simplify your code

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with a feature called 'async await'.

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Now, what is that?

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With that feature, you can turn a function

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into a so-called async function

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by adding the async keyword in front of it.

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Once you do that,

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this function will automatically return a promise

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without you explicitly returning one.

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I have no return statement in this function

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and yet at readFile,

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this function will return a promise now

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because of async.

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Now the async keyword, however, unlocks one other key word,

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which we can now use inside of that async function.

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And that's the await keyword.

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We can add that keyword in front of any method

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that returns a promise.

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Like readFile does here now.

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When we do that, when we do add a weight

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we can get rid of Then,

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and instead store that result in fileData.

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Whoops,

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in that fileData variable, either find here.

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Just as I did it before.

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Even though that's not readFile sync,

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but readFile which returns a promise.

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But under the hood, when using async await,

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JavaScript will add Then to that promise for you,

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and it will provide the value

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which you would otherwise get here as a parameter value

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in this function that's passed to Then,

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to this variable or constant here.

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So JavaScript will give you that value

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as a return value here

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just as if this would be asynchronous operation,

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even though it isn't.

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But it's transformed under the hood,

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behind the scene so to say.

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Therefore,

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you can then get rid of Then here,

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and just execute your other code

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in the very next lines thereafter,

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and code execution will stop until this line here.

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Line 15 is done

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before it advances to the next lines.

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And let me get rid of this part here now.

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Now it is might sound like a step back

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after all we started using async code

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so that we can execute multiple operations

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at the same time.

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But as I mentioned before,

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if you don't have that use case

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and still you are using some operation

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that forces you to use a promise,

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then you can simplify your code again

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with async await like that.

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Now it looks like synchronous code,

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but under the hood,

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that's important,

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it is still translated to this Then version of the code.

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So to that version you saw a couple of minutes ago.

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But to us as a developer,

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this code is now easier to read and write,

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and it looks like synchronous code to us,

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even though under the hood, it's still asynchronous.

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This code here in the end is just put into a Then block

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into a when method called and the anonymous function

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that's passed to then automatically by Java script.

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That's how you can think about that.

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And if you now want to handle errors again,

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since this now again looks like synchronous code.

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You can again use Try Catch as before

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that did not work on the asynchronous code before

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with Callbacks or Promises.

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But when you start using Async Await,

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then Try Catch is available again.

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So that's how you can then handle

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that error you might be getting.

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As a side note if you want to get access

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to the error object,

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that's produced automatically by a readFile

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in case things go wrong.

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You can add a parameter.

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So to say, after a Catch and that will then be available

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in this Catch block.

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And that will be that error object that is produced

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by a readFile.

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That would have been available here before as well

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When we used readFileSync,

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and it's now available again when using async await.

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And that's now the last concept related to async code.

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It allows us to go back to a style

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that looks like synchronous code,

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even though we're still having some async operation.

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And async await can be very useful

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if you want to have that more simplified code,

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And you're fine with not starting multiple async operations

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at the same time,

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because that won't be possible

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because,

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as mentioned,

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Await, now in the end blocks code execution, again,

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until this is done.

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But if you don't need to start multiple operations

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at the same time, then this is a simplification

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that can be useful.