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Debugging Guide for Beginners in Roblox Studio — Transcript

by Driple Studios · 2,692 words · 416 segments · language en · Watch on YouTube

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0:00Hey everyone, welcome back to the
0:01channel. Today's video is for every
0:02beginner developer who has ever stared
0:05at their screen thinking what is my game
0:06broken? I remember reading a comment a
0:08while ago from someone who said that
0:10they were trying to learn game
0:11development through Roblox to try and
0:13earn some money on the side
0:15and put that towards funds for starting
0:17their own business one day. First of
0:19all, that is awesome. But if you are
0:21learning to code, especially as a
0:22beginner, bugs can feel absolutely
0:24impossible to solve and it can be one of
0:26those hurdles that makes people quit.
0:29So, in this video, I'm going to show you
0:30how developers actually fix bugs, the
0:33most common beginner mistakes, and a
0:35step-by-step process that you can use
0:37even if you have absolutely no clue
0:39what's happening. And trust me, every
0:41single developer, even experienced ones,
0:43deal with bugs every single day. The
0:46first thing beginners need to understand
0:47is this, bugs are normal. A bug does not
0:51mean that you're bad at coding, or your
0:53game is ruined, or you should quit.
0:55Professional developers spend hours
0:57debugging, which just goes to show that
0:59really the skill isn't never making bugs
1:01and making perfect code, it's learning
1:04how to use problem solving to overcome
1:07any bugs.
1:08If your game is broken and you are not
1:10checking the output window, you're
1:11basically trying to drive with your eyes
1:13closed. The output tells you your script
1:15errors, any warnings, line numbers, and
1:18sometimes exactly what went wrong. To
1:20open the output, just go to script and
1:22click output. You get this output window
1:25and you can size it however you want,
1:26place it wherever you want. I leave it
1:28at the bottom of my screen.
1:30And now, whenever you press test, any
1:32errors or output logs will appear in
1:35your output window.
1:37I'm going to go through a couple of
1:38example bugs. This first one is a nil
1:40value error. So, the broken code is
1:42local part is workspace.redpart,
1:45part.transparency is 0.5. This script
1:48looks fine, but if the part doesn't
1:50exist, Roblox throws an error. Let's try
1:52it.
1:53RedPart is not a valid member of
1:55workspace workspace.
1:57So, what this really means is Roblox is
1:59trying to find something named red part
2:01inside of workspace. However, when we
2:04run the game, it never finds anything
2:06named red part inside of the workspace.
2:08If we look in the workspace, there is
2:10nothing named red part. Hence, we get
2:12the error, red part is not a valid
2:14member of workspace, workspace. In other
2:17words, red part does not exist inside of
2:20the workspace.
2:22Another error you might encounter, if we
2:23set part equal to nil
2:26and press play,
2:28attempt to index nil with transparency.
2:31So, this is a similar error. This error
2:33means that we are trying to access the
2:35transparency property on part, but part
2:39is nil.
2:40So, let me put this back to how it was.
2:42So, if we are trying to access
2:44transparency on an object that isn't
2:46there,
2:47then we are going to get this attempt to
2:49index nil with error. And that means
2:52that whatever we are trying to access
2:55doesn't exist. So, to fix this, let's
2:58use find first child on red part. We can
3:01do workspace colon find first child red
3:03part.
3:06And this will check if the child exists
3:08or not. If it does, it will return the
3:10part. If it doesn't, it will just set
3:12part equal to nil.
3:13And now we will get that
3:14part.transparency, the attempt index nil
3:17error. So, how can we fix the
3:19part.transparency? We need to check if
3:21the part exists. So, a simple fix would
3:23be to use an if statement. If part then
3:26If the part exists, then we can set
3:28part.transparency
3:30to 0.5.
3:32else
3:34We can put a warning in the output using
3:36the warn keyword, something maybe like
3:39red part was not found.
3:42I'll remove this line now at the end.
3:44Now, when we run this, it says red part
3:46was not found.
3:48So, we've now turned that error that was
3:50breaking the code into something that's
3:52manageable, and this is just a log to
3:54let us know the red part was not found.
3:57So, now instead of crashing, the script
3:59safely checks if the object exists
4:01first. One of the easiest debugging
4:03tools ever is literally just print.
4:07For example, I can type in print
4:10script started.
4:12Now, when I press play, I get a debug
4:15log which says script started.
4:18Beginners often write huge scripts and
4:20have no idea where the problem is. So,
4:22instead, track what's happening. For
4:24example, let's print button clicked.
4:28And then we're going to set coins equal
4:29to 100.
4:31Now, let's print the number of coins we
4:32have.
4:33Let's add 50.
4:37And then let's print the coins again.
4:39Now, when we run this, we have button
4:41clicked 100, then 150.
4:44So, this lets you see
4:46did the code run, first of all?
4:49If button click is printing, then yes,
4:51the code has run.
4:53Did the value change? If the coins here
4:55is different to the coins here, we know
4:57that plus equals 50 has worked.
4:59And which part broke, if any?
5:02A pro tip I would give is to use warn,
5:04because warn is useful because it
5:06appears in yellow in the output window
5:09and is easier to spot. So, rather than
5:11printing coins and printing button
5:12clicked, I could warn button clicked. I
5:15could warn the coins, and I could warn
5:17the coins again. And now it's just a bit
5:19easier to spot in the output. I usually
5:22only use warnings if something genuinely
5:24has gone wrong in the code, and not for
5:26debugging, because a debug is only
5:29temporary. I'm only going to leave a
5:30temporary print in there if I'm
5:33debugging. I'm not going to leave it in
5:34there permanent. I just want to cover
5:36some of the most common beginner bugs.
5:39So, the most common bug that I see in
5:40our Discord server when people are
5:42asking for help and in the comments of
5:43videos, are misspelling names.
5:46This one gets everyone. Let me write
5:48some example code here. Let me add a
5:50part to the workspace.
5:52I'll just leave it named part and I want
5:54to change its brick color to bright red.
5:56I'm going to say
5:57workspace.part.brickcolor
6:01= brickcolor
6:05.new and I'm going to give it bright
6:08red.
6:10Let's run this.
6:12Part is not a valid member of workspace
6:14workspace. But let's look at the
6:16workspace. The part is a valid member of
6:18the workspace. So why am I getting this
6:20error? Well, the reason for this error
6:23we can see it's coming from the script
6:25named buggy code, which is this script
6:27here.
6:28And it's coming on line one. That's what
6:29the colon one means. So it's on line
6:32one.
6:33Let's have a look.
6:35What I can see here, I've misspelled
6:36part. In the workspace, it's p a r t and
6:40in here I've put p a r double t. So
6:42let's remove one of those t's. I'll just
6:43retype it.
6:45And let's run it again.
6:47I'm still getting the error. Part is not
6:49a valid member of workspace workspace.
6:51Quickly pause the video and see if you
6:53can spot what is causing this error.
6:56Hopefully you gave that a go.
6:58So, let's have a look.
7:01As we can see, it's spelled p a r t and
7:03I spelled it p a r t here. However, in
7:05the workspace, I have an upper case p
7:08and in the code, it's all lower case.
7:10The capitalization is very important. It
7:13must match exactly. So I need to have an
7:15upper case p and then all lower case a r
7:17t.
7:18And now if I run this, it will set the
7:20brick color to bright red.
7:22And there we can see that one letter has
7:24broken the entire thing.
7:26This next bug confuses beginners
7:28constantly and that is local scripts and
7:30scripts. Local scripts run on the
7:32player's computer. Normal scripts run on
7:35the server. I'm going to add to starter
7:38player scripts a local script.
7:41And I'm going to say
7:41game.players.playeradded
7:45colon connect
7:47function passing through the player that
7:48joined. I'll just print the player.name.
7:51So, usually in the server script, this
7:53code would run every time a player joins
7:55the server, and it would just print the
7:56name of the player. I'll put this local
7:58script in ServerScriptService.
8:01We can see no output runs.
8:04Now, let's put the local script where it
8:05should be in StarterPlayerScripts.
8:08And we still get no output. And that is
8:10because this is linked to the server.
8:12It's not something that runs on the
8:14player's machine. It runs on the server.
8:17So, this has to be in a server script.
8:19PlayerAdded won't work properly inside a
8:21local script like this.
8:23So, let's put it inside a normal script.
8:25I'm going to add a script to
8:26ServerScriptService named fixed script.
8:30And I'm just going to copy all the code
8:31and paste it into the fixed script.
8:35Now, when we run it,
8:37it prints out my username perfectly.
8:39I'll delete those two scripts now.
8:42Another one is infinite yields. So, this
8:45is a very, very easy one to
8:49notice, but sometimes it can be a bit
8:52hard to figure out why it's happening.
8:54You usually get this when you use
8:56WaitForChild. Let me write local part
8:59equals workspace colon WaitForChild. I'm
9:02going to wait for part.
9:05Now, I don't have a part in my
9:06workspace. Let's just run this and see
9:08what happens.
9:09At first, we don't get anything. After
9:12waiting a few seconds, we get something
9:14that says infinite yield possible on
9:17workspace colon WaitForChild part. If
9:20Roblox says infinite yield possible, it
9:22means the object is taking too long to
9:25appear. Usually,
9:27this means that the object name is
9:28wrong, it was deleted, or it's in the
9:31wrong location.
9:33To fix this, I'm just going to add part
9:35to my workspace. And now, nothing will
9:38output. I'll give it a few seconds and
9:41we won't get that infinite yield because
9:42it will successfully find that part now
9:45in the workspace.
9:47So, infinite yield just means
9:49double-check the object name. It might
9:51be spelled wrong, similar to what we had
9:53earlier in bug one.
9:56It was maybe deleted in runtime by
9:59another script or maybe it's in the
10:01wrong location. Maybe the part we're
10:03looking for isn't in the workspace, but
10:05maybe it's actually in the replicated
10:07storage. The fourth bug I see sometimes
10:10is variables not updating.
10:12Let me write some broken code here. I'm
10:14going to initialize a variable named
10:16zero. It's going to be a local variable,
10:18but it's local to the entire script, so
10:20it's effectively global.
10:22And I'm going to create a local function
10:24and I'll name this add coins. Inside of
10:27this function, I'll say local coins
10:29equals coins plus 10.
10:31This creates a new variable. Now, it's a
10:34bit harder to see what the problem is
10:35here. But, what is happening here is
10:37this is creating a new variable instead
10:40of updating the original. The fix would
10:43be to remove this local keyword in the
10:45function and just do coins equals coins
10:48plus 10.
10:49This changes the original variable
10:51correctly. When we use local in a
10:53function, it's creating a brand new
10:54variable to the original.
10:57Now, let me show you the actual process
10:59that most developers use. The first step
11:01is not to panic. If your game breaks,
11:03don't instantly rewrite everything.
11:06Read the error. That's step two. Read
11:08the error. Most beginners skip this
11:10completely. The output usually tells you
11:13what broke, where it broke, and
11:14sometimes why. Let's review one of those
11:17error messages from earlier. I'm going
11:19to force an error. I'm going to say part
11:22equals nil and then say
11:24part.transparency
11:25equals 0.5. I believe this was one of
11:28our examples earlier. Let's run this.
11:33So, the output tells you what broke. So,
11:36attempt to index nil with transparency,
11:38that's broken. Where it broke? Well, it
11:40broke Well, it broke in the script named
11:42buggy code on line three. You can also
11:44see that just here. It says server
11:46script and it broke on buggy code line
11:49three. So, we're going to look for that
11:51script, which is in server script
11:53service. So, in server script service,
11:55I've got a script named buggy code and
11:57on line three, I'm getting that error.
12:00And sometimes you why it broke. In our
12:02case, it says it's attempt to index nil.
12:04So, that tells me that we are trying to
12:06access the transparency property on
12:08part, but part is nil. So, part doesn't
12:11exist. That is step three as well, which
12:13is finding the exact line. So, line
12:16three.
12:16Step four is to test smaller pieces. For
12:19example, I could print before
12:22transparency, I could print the part
12:24just to make sure a part does exist. And
12:26then afterwards, I could print the part
12:28again just to check if part still exists
12:31after we change the transparency. In my
12:33case, I can see that it prints nil and
12:35then I get the error and the second
12:37print never prints because that error is
12:40preventing it on line five from ever
12:42reaching to line seven.
12:44So, I can see that it's breaking at line
12:46five, but my print part is allowing me
12:49to see that the part is actually nil.
12:51So, that's why I know that part is nil.
12:54I can tell it's wrong based on this
12:56print statement.
12:57A better example would be something like
12:59this. Let's print a statement before the
13:01function call and then print one after
13:03the function call. And if after function
13:06never prints, then you know the problem
13:08happened inside of open door. So, if I
13:11was to run this, after function never
13:13prints. So, we know the problem is
13:15inside of that function.
13:18In my case, the problem here is that
13:19I've not actually defined the function,
13:21so there is no code to run. The fifth
13:23step is just to change one thing at a
13:25time. Beginners often change 20 things
13:27at once, then they don't know what fixed
13:30the bug or what made it worse. Just fix
13:32one thing, test it. If it's still not
13:34working, fix another. If it is working,
13:36then happy days. You don't need to do
13:38much more.
13:39A lot of programming comes down to
13:40keeping a positive mindset, staying
13:42motivated and disciplined to actually
13:44get projects done. The number of
13:46projects I've started and never finished
13:48because I just thought, "Ah, I'm a bit
13:50bored now." Or, "Ah, that code's not
13:52working very well." And that's okay to
13:54have those drop-offs every now and then.
13:57But, the best developers stay
13:58consistent. They learn from their
14:00mistakes. And that is what programming
14:02is all about. It's all about
14:03problem-solving and going from A to B to
14:06C to D. Anyone that makes that jump from
14:08A to Z straight away, well, they're
14:10going to have 24 other letters that are
14:12going to be problematic. Whereas, if you
14:14focus on one letter at a time, one step
14:17at a time, you're going to get there in
14:19a much stronger way.
14:21So, if this video helped you, make sure
14:23to subscribe because we're uploading
14:25Roblox development videos every few
14:27days, as well as expanding to some new
14:29game engines. Comment below what the
14:31most confusing bug is that you've ever
14:33had in Roblox Studio.
14:35Also, join our Discord server, which you
14:37can find the link to in the description,
14:39because the over there you can actually
14:40post if you're having any problems with
14:42your games, if you're having any bugs.
14:45We've got a community of people, and
14:47we're trying to build that community.
14:49And we're all happy to help each other
14:51with our programming over there. You can
14:52also leave feedback on our videos, which
14:54is always highly recommended, and we
14:57really appreciate it. Thanks for
14:59watching, and I will see you in the next
15:01one.

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