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Doing Things With Functions
6:15Commands, or functions, are the basic building blocks of a program. A function lets you define specific steps a computer should take. You then make the computer perform those steps by "calling" the function. Learn about functions while adding to a JavaScript game.
In the last video, I talked a little bit about different
parts of a programming language
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In this video, I'll talk about the basic
building block of a program: a function.
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A function is a collection of code that
"does something." It has a function.
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For example, in our game there's a function to add
items like coins to the screen, to add platforms, to create a badge.
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There are a lot of functions in our game.
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If you'd like to follow along, you can
launch the workspace on this page, or
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continue working with
your previous workspace.
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For example, here's a function
that adds coins to our game.
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There are two steps to using a function,
the first step is creating, or
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what's called declaring the function.
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Declaring a function puts your
programming code into a neat
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little package that's stored in
the computer, or in your browser.
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In JavaScript,
the function keyword creates a function.
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However, the code doesn't do anything
until you call the function,
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that's the second part
of using a function.
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To call a function you use its
name without the function keyword.
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For example,
this function addItems is declared here,
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but it's not called til
way down here on line 84.
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Calling a function makes
the programming inside it run.
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Now, let's call some functions
to make our program do stuff.
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Notice that this function, createItem,
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Is declared here, and it's called up here,
inside of the add items function.
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You can see that we can call functions
from within other [LAUGH] functions.
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Now this may seem confusing but it's very
common in programming to create small
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units of functionality, like these
functions that do just a few things.
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And then call them throughout
the program even inside other functions.
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Now notice that when the create
item function is called,
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there's some information inside
the parentheses, 375, 300 and coin.
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This is information that
we give to the function.
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In programming talk, we say we pass
this information to the function.
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Functions can accept information and
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that information changes
how the function works.
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Let's add another line here, I'll
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type createItem to call the function,
and pass it three pieces of information.
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575, 500, and the string coin,
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I'll save the file and preview it.
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Another coin, as you can see,
calling a function makes something happen.
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If this didn't work for
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you, look carefully at your code,
make sure that it matches mine exactly.
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Even a small error,
like forgetting a comma or
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a quote mark can keep
a program from working.
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Now the numbers here, 575 and 500,
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determine where the coin
appears on the screen.
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The game area is split into coordinates,
at the top,
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is 0,0,
that's at the top left-hand corner.
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From left to right,
we go from 0 all the way up to 800.
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From top to bottom, it goes from 0 to 600.
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The first value is the position
of the coin from the left,
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and the second value is the position
of the coin from the top.
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If we alter any of these values,
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it changes where the coin
appears in the game.
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In fact, I want to move this coin down
a little, so I'll change 300 to 400.
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And you can see the coin has moved down.
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Let's add another coin.
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In fact, I can just copy this, and paste
this code cuz it's pretty much the same,
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just a few pieces of information change.
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Cool, and there's a third coin.
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We can also add more platforms,
let's do that now.
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Platforms are created inside
this addPlatforms function.
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We can add another platform simply
by typing platforms.create,
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calling the function.
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And we'll pass three pieces
of information, 100,
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550, and the string platform.
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I'll save the file, preview it and
we have another platform, super cool.
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Notice that this code looks a little bit
different than the code we did before,
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it has platforms.create.
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This is also a function, but it's a
special type of function called a method.
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It's a function or command that's
provided by the phaser game library.
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Remember we're using a library or
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a bunch of prewritten code that gives
us a lot of tools for creating games.
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Let's add another platform.
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I'll save the file and preview it.
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Nothing's showing up, hm,
I wonder what's going on?
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Let's go back to our code,
there's a slight
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difference between the last line of code
I wrote and the one previous to that.
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Can you spot it?
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There's one character out of place,
this capital C.
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It seems like a small difference, but
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as I mentioned earlier,
programming languages can be pretty picky.
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You have to type things exactly right or
a program won't work.
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JavaScript code, like a lot of
programming languages, is case sensitive.
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Meaning that create
with a lower case c and
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Create with an upper case c
mean two different things.
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It's an easy fix fortunately,
you just change this to a lower case c.
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I'll save the file and
preview it, cool, it works.
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Why don't you spend a few minutes adding
more coins and platforms to this game.
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Let's see if you can create
something that looks like this.
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Has nine platforms and nine coins.
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In the next video,
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I'll show you how we can customize
the game even more with some new graphics.
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But, in the meantime,
why don't you try another code challenge?
6:12