Hey guys, welcome back. This is the big video on functions. So, when I say
function what I mean is it's a block of code that's not run but that you can
reference in your code to have it run, and you can supply it certain data as
you do so. Now that explanation might seem a little obscure, so let's
just jump into it. Much like when you create a variable you use the keyword
var, when you create a function you're going to use a keyword called
function, and then space. And here you're going to give your function a name. So,
for instance, mine is going to be myVar. You guys can name this whatever you want.
At this point, once you have it named, you need to open up and close curly brackets
and then you can put arguments in here, and we're going to talk more about that
later, but for right now on the right hand side at the very end of the line as
of this point, after the closed brackets, open up the curly brackets, and close
them. This is a function. Right now this function is empty, but you guys have
written a function. So, let's make this not empty. I'm going to console.log "My
name is nick." Now I'm going to save this, and refresh our page here, and nothing
happens because we didn't call the function. So this is defining a function,
this is building a function, but then to call the function
remember when we alerted information on the page when you first loaded it
we called alert, and that's how you call a function. You just write the
function name, I actually named it at myVar, let me name it myFunction. So down here
I'm going to call the function, and by calling it I mean I'm going to tell it
to do it's thing to run. So I'm going to type myFunction, and then we're going to
open and close the brackets, and there's no parameters to be passed in
here, it's just a function in and of itself. So I'm just going to end the line
with a semicolon. I'm going to save and refresh,
and it prints out my name is nick because I've told it to right here.
Now, when I say arguments you can actually pass an argument into that. Let
me erase this. Let's create a new function called printName. So, we're
going to take in one variable, or one bit of data, that we're going to reference
inside of the function as a variable and it's going to be name. Now open up and
close your curly brackets, and in here we're just going to print out hello and
then name. So, console.log and here we're going to open up quotations "hello"
and then a comma. And then outside of the quotations instead of concatenating it
with a plus sign, we're going to concatenate it with a comma. And it's not
really concatenation, it doesn't make it the same thing, but it prints out both of
these, one and then the other. So, like that. Now by using a comma I don't have
to make sure there's a space hard-coded at the end of that line. This essentially
adds one. So, down here let's call print name and let's pass it an argument. Now,
within the function here we're using it as a string. We can't send it as a...I mean
we could set it as a boolean if we wanted to. But, name is going to be Nick, end that
with a semicolon, save it, refresh our page, and it says hello Nick.
Now I can call that function again and give it a different name, Charles. And now
it's going to print Nick and then Charles. So as you can see whatever we pass as
the value when we call the function becomes this inside of the function, and
so that's a very quick look at parameters. You can add multiple
parameters in which case you just comma separate them. So, age and
then I'm going to put a comma here, and a period. So we're going to end that
statement and then say you are, and then their age separated by comma. So this says
hello name, you are age. So when we call the functions now...if I just save it and
run it it will not work because it says you are undefined, because we haven't
defined anything in these function calls. So let's say 28 separated by a comma again,
and then space 56. Save it and refresh, and you can see that it says hello Nick
you are 28 because we're passing both of these values in so this becomes name, and
this becomes age. You generally need to pass them in to the function in the same
order that they are expected to be in I guess, which you guys could probably
guess that. So this is a quick way to add a function. We're going to be covering
functions more in depth and the main reason why we use them. We use them so
that we can write out a big long function here, and then if we need to you
know pull it off multiple times. So let's say we're logging in a user that's like
a 20 lines of code. So, rather than logging someone in manually and
writing out the code in like 10 different spots, let's just create a
function then call that function from those 10 different spots, and that's why
we use functions. So, in the next video, we're going to be diving deeper into
functions and learning more about them.