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So now we've got

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some key basics about functions,

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but we're still not done

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because this function is still not ideal,

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it's still not perfect.

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It works but we have a couple of bad practices in there,

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which we don't typically wanna do.

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I did explain why we can change adult years

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if our code looks like this.

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But maybe you get the feeling over the last lecture that

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that's a lot to memorize,

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and it is.

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And sometimes you need this behavior,

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which I described,

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that you can shadow variables

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and that you don't wanna do it in other scenarios

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but you can also make life easier for you.

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It would be best if this function doesn't even have to know

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about the variable name of our outside variable here,

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if it could work stand alone.

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Because at the moment,

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if I ever changed this from adult years to,

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let's say total adult years,

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I have to change this name down here

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and down here,

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and also inside of the function.

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And again,

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because this is a simple script

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that's not too difficult.

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But you always have to keep in mind

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that ultimately you will write more complex code

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and then having to make changes,

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in dozens of places,

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maybe even across multiple JavaScript files,

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is very annoying.

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So therefore,

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it would be better if this function

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wouldn't even have to know this external variable name.

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And indeed that is something you typically wanna strive for,

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that your functions work

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without knowing external variable names.

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And when it comes to deriving this result here,

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this result of this calculation,

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what we can do in a function

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is we can return the result of a calculation

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with the special return keyword.

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Now, what does returning a value mean?

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It means that this function does now

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not just perform a certain operation

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or possibly multiple steps.

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You can have multiple lines of code in there,

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that would be fine.

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But that instead when you call that function,

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you now get a value from calling that function.

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So before this function,

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without the return keyword,

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didn't return anything.

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Calling that function doesn't produce a new value.

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Now with the return statement,

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calling that function does produce a new value

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and calling that function does return this result.

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Hence, we can work with that result here

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in the line of code where we called this function.

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And we can, for example,

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store it in a variable again.

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In total adult years, for example.

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Here we can store the result of calling that function.

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Now, of course,

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that still means we're using

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that variable name down there.

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And if we were to change it,

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we have to change it in these places down there.

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But it's very often the case

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that you store functions like this in separate files.

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And then you at least

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don't have to dive into those files as well,

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to make such variable name changes.

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And in your main file

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where you are using a variable

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in different places in your code,

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you can always use the search

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and replace feature of your IDE of Visual Studio Code,

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to quickly change the name in all the places

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where it needs to be changed.

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So this typically is a better way of doing it

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than what we did before.

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And in addition

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and even more importantly than this,

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we don't have to change the name everywhere thing,

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we now also made a huge step

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towards making our function more reusable,

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more flexible.

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Before we returned,

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we always stored the result

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of our calculation in total adult years,

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inside of that function.

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And that means

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that if we ever would want to use

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this function in a different place of our code

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and store the result in a different variable,

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it's just wouldn't work,

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as long as we directly referenced total adult years

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from inside this function.

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Now with the return statement that changed,

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now we can use this function anywhere in our code

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and in the place where we use it.

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So in the place where we call this function,

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we can then decide where the result should be stored.

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And that is a huge benefit of using the return statement,

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instead of directly accessing a variable in the function

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and storing our value there,

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because now our function is more reusable and more flexible,

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even though that's not something we utilize

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or need for this simple demo here.

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But it is something you typically wanna go for

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when you write code.

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Because ultimately,

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it will make your life as a developer easier.

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We also of course,

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wanna do that down here,

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where I call calculate adult years again.

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Because we now need to store that return value,

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otherwise that returned value goes into the void

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and we won't be able to work with it.

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Now, if I save this again,

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I again get these alerts with 14 and 27.

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Let me close this and reload

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to make that a bit easier to read.

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And that's a great step forward

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and a very important feature,

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functions don't have to return the value.

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For example, alert here doesn't return a value.

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We're not storing this anywhere,

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but they often do.

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And especially if you have a function

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that performs a certain mathematical operation,

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it's very common that you do want to return

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so that the result of this operation

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then can be stored in different variables in your code.