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Now in the last lesson we looked at the chocolate flavor of functions, which are functions that are able
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to take an input and use that input inside the function to do some calculation or to use it as a part
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of the code.
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Now in this lesson, I want to show you an even more complex and also more useful type of function, which
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are functions that are able to give an output.
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So for example, taking the previous example where we're able to take money as an input to the function
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and use it to calculate the number of bottles of milk that we can buy, at the end of the code we can
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use the keyword return to specify that this function, in addition to being able to take inputs,
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it can also give an output.
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And in our case we're giving the output of money modulo 1.5.
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So remember that 1.5 is the cost of a bottle of milk.
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So money modulo 1.5 means that we're getting the remainder of how much we've spent to buy the milk.
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So, if you remember, the modulo works like this. Whereas 9 divide by 6, 6 only goes into 9 once.
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So we get a remainder of three.
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So in this case the variable e is equal to 3, because the modulo gives you the remainder of the division.
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So in this function if we gave an input of $4 and each bottle of milk cost $1.5 then the robot will
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buy 2 bottles of milk which will cost $3 and it'll give us $1 change. And that $1 of
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change is the output from this function which we can bind to a variable called change.
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So, for example, we can say variable change is equal to the outcome of the function
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getMilk with an input of 4.
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And change will equal 1, because remember each bottle of milk costs 1.5.
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So $4 only gets you two bottles of milk which costs $3 and that gives you a remainder of 1.
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So now the output of this entire function is equal to 1,
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and that gets assigned as the value to the variable change. That might take a little bit to sit in.
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But let's just review creating the function, this third type of function.
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So the important things are we have the function keyword that specifies we're creating a new function.
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We have to give the function a name straight afterwards and then inside the curly braces we specify
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whether or not if we have an input that this function is going to use.
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And in order to get an output out of the function we have to use that keyword return, and whatever gets
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returned in the function becomes the right hand side of this function call.
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So when we call a function that has an output we can use the output and we can assign it to a variable,
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for example in this case the variable change.
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So if we didn't have this line where we have a return statement or specify that our function has an output,
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then calling getMilk only executes the function without getting an output back.
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So this is the most complex of all three functions.
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And this is the last flavor that we're looking at, which is the strawberry flavor, which incidentally
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is also the flavor that I never touched because it tastes awful.
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But our third function doesn't have to be awful as long as we understand how the return works.
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So let's take a look at this in practice.
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So currently we've got a function that takes an input called money, and it uses that input to calculate
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how many bottles of milk we're able to buy using that money.
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But at the end of the function, just before we hit the closing brace, we can add a return keyword and
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specify that we want this function to output a number and the number is going to be money modulo 1.5
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which is the cost of a bottle of milk.
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So this will give us the remainder of this division.
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So that means that if we give say an input of 3, 3 divided by 1.5 has a remainder of 0.
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So we'll end up returning 0. But if we gave it a value 4, then we will have a remainder of 1, and that
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number 1 becomes the output of this function call.
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So we can capture it and save it inside a variable called change, for example, and I can log the value
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of change by writing console.log(change).
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So now if I hit run you can see that all of those lines of code get executed and it shows me that I'm
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buying two bottles of milk but it also shows me that I'm getting a change of one and that comes from
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this return statement.
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So this is quite useful because it allows us to use a number of functions inside other functions.
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So for example if, instead of messing up my bunch of instructions, I took this part where I calculate
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the number of bottles of milk I get based on money into its own function.
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So, for example, let’s create a function called calcBottles, and it takes an input in the form of startingMoney
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and also costPerBottle.
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So we can now say that the number of bottles is equal to this input called startingMoney divided by
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the costPerBottle,
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right?
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This is always going to be the same calculation that you need to perform no matter which scenario.
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So you could have a starting money amount of $5 $10 $20.
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It doesn't matter.
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And if you divide that by the cost per bottle of milk then you will end up with the number of bottles.
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So now, how can we use this function inside here?
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Well, if we give this function a return statement, and we say that the output of this function is the
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number of bottles, then up here we can write console.log “buy “ + calculate bottles using the amount
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of money we got as an input over here as the first parameter, which is startingMoney,
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and the second input, 1.5 as the second parameter, which is the cost per bottle, and now, once our code
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gets to this line, which is line number 12, then it’ll go and find where this function was created, calcBottles,
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which is down here of course,
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it will place the value of money into startingMoney, 1.5 into costPerBottle, and it will calculate
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the number of bottles.
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And once it gets to this return statement, that value in numberOfBottles will replace this part of
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the code because it is the output of the function.
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So now if I call my first function getMilk and I specify an input of say $5, then that $5 is going to
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go into this parameter called money and then it's going to move over here in order to use it to calculate
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the number of bottles we’ll get back.
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So if I hit run you'll see that all of the instructions are executed and it also tells me that I'm able
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to buy 4 bottles of milk and have 0.5 as the change.
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Now what if we did the same thing down here?
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What if, instead of doing the calculation in here, we created another function, and we called this function
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calcChange, and the inputs that it's going to take is startingAmount and also costPerBottle.
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And inside this function I'm going to calculate change, which is going to be equal to startingAmount
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modulo costPerBottle.
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And that is what I'm going to return as the output of this function.
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So now, instead of returning this calculation, I can simply return calcChange, and the first input is
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going to be money,
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and the second input, costPerBottle, is going to be 1.5, and that becomes the output of this function,
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which is getMilk.
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So instead of just calling getMilk here, I can also say console.log, call this function getMilk,
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and we're going to add it to a string,
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so we're going to say “Hello master,
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here is your “
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whichever amount that you get + “ change.”.
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So now if I run the code you can see that it goes through all of the commands, buys 3 bottles of
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milk,
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and finally we get “Hello master, here is your $0.5 of change.”.
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So as you can see what we're doing here is we're using the outputs of functions in order to use it inside
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other lines of code.
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So now, say if the cost per bottle of milk changed,
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right?
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Say it now costs $2.5 instead of 1.5.
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Then we don't have to change the calculation.
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And in fact we can make this even more dry by reducing the repetition inside the function.
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So as an input we can say getMilk, the amount of money as an input and also the cost per bottle as an
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input,
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and we can replace that hit.
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So now, when we call getMilk, we have to say the amount of money we got given is 5 and the cost per
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bottle is say 1.5.
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So this will give us 3 bottles of milk and 0.5 change, but say tomorrow the master gives
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us $10 to buy milk,
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and the cost of milk has gone up to $3, and now we're able to only buy 3 bottles of milk but we get
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$1 change.
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You will find yourself using all three types of functions in a variety of scenarios depending on what
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it is that you're trying to do.
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There's a lot of new information that you've learned.
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So it's really really crucial that you try to understand this information by completing some exercises
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and trying to write the code yourself.
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So in the next lesson I have an interactive challenge for you where I want you to write some code and
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we'll use some software on our site to test your code and see if you got it right.
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So for all of that and more exciting stuff, I'll see you on the next lesson.