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Welcome back.

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Today, we going to talk about JavaScript functions, how we can declare war on, how we can call one,

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how we can execute a function in what function expression means.

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OK, let's start working.

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So create a lecture five file inside, put a node call and call it JavaScript function.

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Now, also here, make sure that you linking that file to external file.

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That's why we need to link.

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Now we have used two functions so far.

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The first one was alert in the second one was prompt.

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Actually, this was the first one.

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This was the second one.

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But that doesn't matter.

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So if we go to a browser and we type prompt and if you hit enter just like this, don't put the brackets,

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it will say it's a function if you put alert.

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Oops, Leard.

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It's F stands for function, but what are these brackets, let's use them.

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Wow, now you see that we are calling and executing the function, right?

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That is pretty much it.

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So these oops, sorry, these let me just show you this.

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These brackets means call and execute the function.

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And we usually do them like this.

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That means end of an expression, because when we are one to end expression as explained, if you don't

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know, just watch the previous lecture or two lectures, I'm not sure, but just explain what the expression

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means and why we need to end it.

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OK, but we are not going to use this inbuilt functions.

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We're going to create our own.

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So let's create our first own function in.

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Let's declare it.

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Clear a function, so F stands for function.

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It's a shortcut, so we need to use the key word function.

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That's the Goldway my first.

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Function and this is my name, I can name it the functions that I want, you can put here my 100 my

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my this is my thousand function.

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Whatever you want to be here, my name, whatever you makes you happy.

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But I just put it here because it makes sense.

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Now, in order to know that it's a function, we need to use this parentheses and this curly brackets

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means a block of code will go here.

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Now console the lock I'm going to use here and I will say so you're going to say hello from here.

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Save it now if you go back.

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I need to use this.

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If you go back, refresh here, you're not going to see the result in.

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Why is this?

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Well, because we need to call it function.

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So we just declared a function.

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But we now need to call the function by calling the function with these brackets.

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It will actually mean call the function and execute.

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Now go back.

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There you go.

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That is pretty much it.

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Now, what is more interesting, a function can have one or more arguments.

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Now you will see that this is mixed up with parameters.

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Uh, spelled it right, right.

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So arguments and parameters, but.

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You don't have to worry about if you mixed these as well, because in old tutorials or books, you will

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see that they used arguments and parameters.

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But I want you to know the read the reality so functions can take arguments in what are the arguments?

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Well, we already use them.

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These were the arguments for the alert alert rackets and high.

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So it would it take one argument that this string this is this is and maybe I didn't tell you back then,

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but because we haven't done the functions now there is the time.

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So I'm going to create a second function called.

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My second, actually, let's put it like this function argument function, and you can put any name

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meaningful that you want in here, we will see first argument.

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Very good.

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Now, you can give any name of the argument and let's say control that log.

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The argument only I'm just.

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First argument, whatever we passing to the function, that's how you call it, you passing an argument

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to a function you're going to control.

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So I'm going to just print it out.

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So what are we going to do now?

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Argument function.

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Very good.

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And now we need to pass that one so it can be screened.

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It can be boolean, it can be any data that you JavaScript type that we have encountered so far.

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But I'm going to say hello.

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I'm just going to pass a screen and I'm going to save it.

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In there you go.

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This is the helo that I passed to the function as an argument.

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So even if I changed this to just a but I need to call it here as well, A, that it will still work.

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This is irrelevant.

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What we put here, every name we put here, it's irrelevant.

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But what is relevant, what we are passing to function.

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Now, this is one argument function, whatever.

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What if we have more arguments?

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Let's create a function that will take multiple arguments.

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For example, let's create a function that will calculate the year that we are born.

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So function.

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Bert.

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Birth year and coup, you can name it whatever you want, first parameter will be your age and now inside

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I will see your birth year

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again.

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I'm naming variable as I want.

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You can just change the name.

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Now, I just want to say a year minus age.

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So whatever we passing to the function here, when we call it, we're.

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Here and here, we can pass directly 20, 20 to say 23, cool.

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Now the Bertier will get the result of 20, 20 to minus at the age.

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Nice.

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So console at last.

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The birth year.

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Save it.

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Very good.

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We do have the result.

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One more thing that I want to show you is that, oh, actually, I didn't see this.

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When we have multiple arguments, we need to space them with comma.

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Same as here.

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Very good.

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Now, what is function expression?

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And this is very important for you to understand.

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Well, let's create a variable called function expression, and that will be equal to a function.

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Oops.

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And comes along.

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Function.

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Here.

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Now, this is coming from function expression, very good.

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Now, what is happening here?

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Well, we declare a variable.

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And this equal sign, it's not the same as Inmet, this equal sign means these equal means assign a

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value to something, right?

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So whatever this function returns, we will assign it as a value of this function.

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But now dysfunction doesn't have a name.

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It's called anonymous function.

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Now, the function that they don't have any name, it's called anonymous function.

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And this is the beauty of function expression.

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Now, there are examples where you can see here we can declare the name, but I'm not going to do that

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because those examples are very rare and you don't need them.

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OK, so how are we going to call a function without name?

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Well, we can use the variable name.

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How cool is this?

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I'm in the mood today, and that's it.

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We don't have any arguments, but we can have one or two or many arguments here as well.

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Same as the other ones.

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Let's see.

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Save it, boom.

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There you go.

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The cons a lot.

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Nice.

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So one more thing that I want to show you two more things that I want to share with you tonight and

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is that that we are at the moment consoling the output.

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And if we remove this one, this nineteen ninety nine, it will be gone, it's nothing, dear.

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And why is this?

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While console lock is just for us, we printing the values here to be able to see it so the user can

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see it.

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But the result of this function is stored nowhere.

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Right.

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So what's the solution?

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OK, I'm going to copy this one scan uncommon.

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This one.

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Return, I'm going to use return nouse, so Bourdier, one word here, one in here, instead of calling

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lot, I'm just going to say return the bird here.

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So what do you think it will happen now?

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When I call this function here with these two arguments, it will go inside, it will do its job, do

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it calculation and it will return the result of this, whatever it's taught here.

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But how I'm going to access it outside, because if I do it right now, there's no another nineteen

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ninety nine and I want so these Bertier actually now can be canceled.

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Look again.

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That's the one way.

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It's.

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My hands are not working tonight, so there you go, but this is no different than it was here, right?

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We can be better than this.

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Of course.

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So I'm just going to comment on this one.

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But this bad boy here.

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So I'm going to see more result or I'm just going to say birth year needs more meaningful like that.

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And I'm just going to put here the function.

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I'm going to call the function with the two parameters.

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Let's make it 20, 23.

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So that will return a different year and now we need to cancel a log this birth year because the result.

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Oh, now I do have a problem.

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See, I have used bird ear and bird ear as a function.

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Now, we can't do that.

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So bird ear result.

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We can't call a function and the variable.

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Same name.

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Two thousand nights, it's our function is working, so in this budget year result, we have stored

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the value of dysfunction and we can use it now.

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For example, if I want to subtract one year minus one year, make a breathing space, there it is so

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we can reuse it.

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That's called code reusability.

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Now, return is a key word and it's.

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We can't use it as a variable, so even we have this different color, it's a purple for the function

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and for the variables, we also have a little bit different color and for the functions name.

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Nice.

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So this is predefine key keyword that we're not going to be able to use.

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It's taken.

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Right.

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Nice.

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So let's do one more thing.

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And this is a final.

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I promise.

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So let's create a function that will take four parameters.

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Nice.

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Now we are talking, but we will use this Bergère function inside the function.

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So that's mean.

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We can call the function from a function so we don't need this.

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So function name the new function.

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Name will be print details.

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Nice.

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This is good function name.

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So it will take first name as an argument, last name and year and age.

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Now this year and age we will use them and we will supply to this function.

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But the first two that's actually been these days, it's so consulate lock we will use for these print

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details.

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So my first name is we're going to read Spazz there plus first name and what I haven't shown you what

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we can do a new line just like this.

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Now, compare this to more times, my last name is Make sure you change here, the last name, this

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variable, whatever we pass as an argument.

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And now.

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I am born oops in and we can say here we can call the function birth year that's called the function

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birth year one and pass year and age nice.

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Save it.

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So what what else we need to do is just to call print details and now you see how these two functions

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will work.

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So this function will start doing these line, then the second line and it will stop here and it will

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do the calculation of this.

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OK, so we need to just pass in some details with your details if you want.

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So don't put my right.

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It's not good.

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Make sure that you put in your own details.

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And we are just putting twenty, twenty two here and thirty three and save it.

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And let's see.

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There you go.

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This is the result.

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So now you know how to call function from inside a function.

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So I will see you in the next one.

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And we are done for tonight.