Script an upgrade button

Players can now collect coins and lose them when they die, but the coins don't do anything, and most of the 3D world is inaccessible without the ability to jump very high. This section of the tutorial teaches you how to finish the logic for your game by adding an on-screen button that spends coins to increase jumping power.

Create the upgrade button

2D interfaces in Roblox are typically made up of a collection of GUI components inside of a GUI container. In this case, you only need a TextButton component that says Upgrade Jump (5 Coins) inside a ScreenGui container.

Build with Assistant

In ReplicatedStorage, create a folder named Instances.

Inside the Instances folder, create a ScreenGui named JumpPurchaseGui with ResetOnSpawn disabled.

Inside JumpPurchaseGui, create a TextButton named JumpButton with the following properties:
- Text: "Upgrade Jump (5 Coins)"
- TextSize: 25
- AnchorPoint: 1, 1
- Position: {1, 0}, {1, 0}

Also inside the Instances folder, create a RemoteFunction named IncreaseJumpPowerFunction.

Finally, on the StarterPlayer service, enable the CharacterUseJumpPower property.

Build it Yourself

For the upgrade button, you'll create a folder inside ReplicatedStorage to hold the upgrade system, including a ScreenGui that contains the button and a RemoteFunction that clients use to request upgrades from the server. Storing these objects in ReplicatedStorage makes them accessible to both clients and the server.

In the Explorer, hover over ReplicatedStorage, click ⊕, and insert a folder. Rename it Instances. This is where you'll keep shared objects that the client and server both need.
Insert a ScreenGui into the Instances folder. In the Properties window:
1. Set Name to JumpPurchaseGui.
2. Disable ResetOnSpawn so the GUI doesn't get wiped when the player respawns.
Insert a TextButton inside JumpPurchaseGui and rename it JumpButton. In the Properties window:
1. Set Text to Upgrade Jump (5 Coins).
2. Set TextSize to 25.
3. Set AnchorPoint to 1, 1.
4. Set Position to {1, 0},{1, 0}.
Back in the Instances folder, insert a RemoteFunction and rename it IncreaseJumpPowerFunction. Remote functions need to live in ReplicatedStorage so the client and server can both reference them.
Select StarterPlayer in the Explorer, then in the Properties window enable CharacterUseJumpPower. Without this, jump power values are ignored and every character jumps at a fixed height.

Define jump power data

Currently, only coin count is stored for each player in the PlayerData module script. You need to also store and update jump power in the same way. Because the functions in PlayerData are non-specific to the data being changed, all that's required to store player jump power is to add a Jump key and initialize its initial value in defaultPlayerData().

Build with Assistant

In ServerStorage, replace the existing PlayerData ModuleScript's code with the following:

```lua
local PlayerData = {}

PlayerData.COIN_KEY_NAME = "Coins"
PlayerData.JUMP_KEY_NAME = "Jump"

local playerData = {
	--[[
		[userId: string] = {
			["Coins"] = coinAmount: number,
			["Jump"] = jumpPower: number
		}
	--]]
}

local function defaultPlayerData()
	return {
		[PlayerData.COIN_KEY_NAME] = 0,
		[PlayerData.JUMP_KEY_NAME] = 0,
	}
end

local function getData(player)
	local data = playerData[tostring(player.UserId)] or defaultPlayerData()
	playerData[tostring(player.UserId)] = data
	return data
end

function PlayerData.getValue(player, key)
	return getData(player)[key]
end

function PlayerData.updateValue(player, key, updateFunction)
	local data = getData(player)
	local oldValue = data[key]
	local newValue = updateFunction(oldValue)

	data[key] = newValue
	return newValue
end

return PlayerData
```

Build it Yourself

In the Explorer, open the PlayerData ModuleScript inside ServerStorage.
Replace its code with the following code to add a JUMP_KEY_NAME constant and initialize Jump to 0 so that every new player starts with zero jump power:

local PlayerData = {}

PlayerData.COIN_KEY_NAME = "Coins"
PlayerData.JUMP_KEY_NAME = "Jump"

local playerData = {
	--[[
		[userId: string] = {
			["Coins"] = coinAmount: number,
			["Jump"] = jumpPower: number
		}
	--]]
}

local function defaultPlayerData()
	return {
		[PlayerData.COIN_KEY_NAME] = 0,
		[PlayerData.JUMP_KEY_NAME] = 0,
	}
end

local function getData(player)
	local data = playerData[tostring(player.UserId)] or defaultPlayerData()
	playerData[tostring(player.UserId)] = data
	return data
end

function PlayerData.getValue(player, key)
	return getData(player)[key]
end

function PlayerData.updateValue(player, key, updateFunction)
	local data = getData(player)
	local oldValue = data[key]
	local newValue = updateFunction(oldValue)

	data[key] = newValue
	return newValue
end

return PlayerData

Update jump power data

Now that PlayerData is able to track jump power, you need to implement logic on the server to upgrade jump power from a player's client request.

The server and client can communicate through either RemoteEvents or RemoteFunctions. Remote events don't yield when they're fired and can be used for one-way communication. Remote functions, on the other hand, yield until they receive a reply, which allows for two-way communication.

For this tutorial, the client needs to know if the server upgraded the player's jump power successfully, so you should use a remote function.

Build with Assistant

In ServerScriptService, create a Script named JumpService with the following code:

```lua
-- Services
local ReplicatedStorage = game:GetService("ReplicatedStorage")
local ServerStorage = game:GetService("ServerStorage")
local Players = game:GetService("Players")

-- Modules
local Leaderboard = require(ServerStorage.Leaderboard)
local PlayerData = require(ServerStorage.PlayerData)

-- Events
local IncreaseJumpPowerFunction = ReplicatedStorage.Instances.IncreaseJumpPowerFunction

local JUMP_KEY_NAME = PlayerData.JUMP_KEY_NAME
local COIN_KEY_NAME = PlayerData.COIN_KEY_NAME
local JUMP_POWER_INCREMENT = 30
local JUMP_COIN_COST = 5

local function updateJumpPower(player, updateFunction)
	-- Update the jump power table
	local newJumpPower = PlayerData.updateValue(player, JUMP_KEY_NAME, updateFunction)

	-- Update the players jump power
	local character = player.Character or player.CharacterAdded:Wait()
	local humanoid = character:FindFirstChildWhichIsA("Humanoid")
	if humanoid then
		humanoid.JumpPower = newJumpPower

		-- Update the jump leaderboard
		Leaderboard.setStat(player, JUMP_KEY_NAME, newJumpPower)
	end
end

local function onPurchaseJumpIncrease(player)
	local coinAmount = PlayerData.getValue(player, COIN_KEY_NAME)
	if coinAmount < JUMP_COIN_COST then
		return false
	end

	-- Increase player's jump power
	updateJumpPower(player, function(oldJumpPower)
		oldJumpPower = oldJumpPower or 0
		return oldJumpPower + JUMP_POWER_INCREMENT
	end)
	-- Update the coin table
	local newCoinAmount = PlayerData.updateValue(player, COIN_KEY_NAME, function(oldCoinAmount)
		return oldCoinAmount - JUMP_COIN_COST
	end)
	-- Update the coin leaderboard
	Leaderboard.setStat(player, COIN_KEY_NAME, newCoinAmount)
	return true
end

local function onCharacterAdded(player)
	-- Reset player's jump power when the character is added
	updateJumpPower(player, function(_)
		return 0
	end)
end

-- Initialize any players added before connecting to PlayerAdded event
for _, player in Players:GetPlayers() do
	onCharacterAdded(player)
end

-- Normal initialization of players from PlayerAdded event
local function onPlayerAdded(player)
	player.CharacterAdded:Connect(function()
		onCharacterAdded(player)
	end)
end

local function onPlayerRemoved(player)
	updateJumpPower(player, function(_)
		return nil
	end)
end

IncreaseJumpPowerFunction.OnServerInvoke = onPurchaseJumpIncrease
Players.PlayerAdded:Connect(onPlayerAdded)
Players.PlayerRemoving:Connect(onPlayerRemoved)
```

Build it Yourself

In the Explorer, insert a new Script into ServerScriptService and rename it JumpService. This script holds the server-side logic for the jump upgrade: it receives the request, charges coins, and updates the character's JumpPower.
Replace the default code with the following:

-- Services
local ReplicatedStorage = game:GetService("ReplicatedStorage")
local ServerStorage = game:GetService("ServerStorage")
local Players = game:GetService("Players")

-- Modules
local Leaderboard = require(ServerStorage.Leaderboard)
local PlayerData = require(ServerStorage.PlayerData)

-- Events
local IncreaseJumpPowerFunction = ReplicatedStorage.Instances.IncreaseJumpPowerFunction

local JUMP_KEY_NAME = PlayerData.JUMP_KEY_NAME
local COIN_KEY_NAME = PlayerData.COIN_KEY_NAME
local JUMP_POWER_INCREMENT = 30
local JUMP_COIN_COST = 5

local function updateJumpPower(player, updateFunction)
	-- Update the jump power table
	local newJumpPower = PlayerData.updateValue(player, JUMP_KEY_NAME, updateFunction)

	-- Update the players jump power
	local character = player.Character or player.CharacterAdded:Wait()
	local humanoid = character:FindFirstChildWhichIsA("Humanoid")
	if humanoid then
		humanoid.JumpPower = newJumpPower

		-- Update the jump leaderboard
		Leaderboard.setStat(player, JUMP_KEY_NAME, newJumpPower)
	end
end

local function onPurchaseJumpIncrease(player)
	local coinAmount = PlayerData.getValue(player, COIN_KEY_NAME)
	if coinAmount < JUMP_COIN_COST then
		return false
	end

	-- Increase player's jump power
	updateJumpPower(player, function(oldJumpPower)
		oldJumpPower = oldJumpPower or 0
		return oldJumpPower + JUMP_POWER_INCREMENT
	end)
	-- Update the coin table
	local newCoinAmount = PlayerData.updateValue(player, COIN_KEY_NAME, function(oldCoinAmount)
		return oldCoinAmount - JUMP_COIN_COST
	end)
	-- Update the coin leaderboard
	Leaderboard.setStat(player, COIN_KEY_NAME, newCoinAmount)
	return true
end

local function onCharacterAdded(player)
	-- Reset player's jump power when the character is added
	updateJumpPower(player, function(_)
		return 0
	end)
end

-- Initialize any players added before connecting to PlayerAdded event
for _, player in Players:GetPlayers() do
	onCharacterAdded(player)
end

-- Normal initialization of players from PlayerAdded event
local function onPlayerAdded(player)
	player.CharacterAdded:Connect(function()
		onCharacterAdded(player)
	end)
end

local function onPlayerRemoved(player)
	updateJumpPower(player, function(_)
		return nil
	end)
end

IncreaseJumpPowerFunction.OnServerInvoke = onPurchaseJumpIncrease
Players.PlayerAdded:Connect(onPlayerAdded)
Players.PlayerRemoving:Connect(onPlayerRemoved)

Code explanation

The following sections describe the code in more detail.

Update the jump power data - updateJumpPower() updates the jump power of the player and the leaderboard to provide visual feedback. This function resembles the code that damages players in Create player hazards. Provided a Character model and Humanoid exist for the player being upgraded, the function updates the JumpPower property to the new value stored by PlayerData, increasing it by 30. If you want your game to last slightly longer, you can decrease this number.
Validate server requests - onPurchaseJumpIncrease() first checks that the player actually has the number of coins required to purchase the upgrade. All requests from clients to the server should be validated to prevent bad actors submitting false requests and exploiting your game.

Add the button to the player GUI

A ScreenGui object only shows on-screen if it is parented to a player's PlayerGui object. By default, this contains the system GUI such as the chat window. You now need to create a script in ReplicatedStorage to copy the upgrade button into each player's GUI and implement behavior for when the button is pressed.

Build with Assistant

In ReplicatedStorage, create a Script named JumpButtonClickHandler with RunContext set to Client and the following code:

```lua
local ReplicatedStorage = game:GetService("ReplicatedStorage")
local Players = game:GetService("Players")

local player = Players.LocalPlayer
local playerGui = player.PlayerGui

local IncreaseJumpPowerFunction = ReplicatedStorage.Instances.IncreaseJumpPowerFunction
local jumpPurchaseGui = ReplicatedStorage.Instances.JumpPurchaseGui
local jumpButton = jumpPurchaseGui.JumpButton

local function onButtonClicked()
	local success, purchased = pcall(IncreaseJumpPowerFunction.InvokeServer, IncreaseJumpPowerFunction)
	if not success then
		-- purchased will be the error message if success is false
		error(purchased)
	elseif success and not purchased then
		warn("Not enough coins!")
	end
end

jumpButton.Activated:Connect(onButtonClicked)

-- Add the JumpPurchaseGui to the player's Gui
jumpPurchaseGui.Parent = playerGui
```

Build it Yourself

In the Explorer, insert a new Script into ReplicatedStorage.
With the script selected, in the Properties window:
1. Set Name to JumpButtonClickHandler.
2. Set RunContext to Client. This tells the engine to run always run this script on the client to optimize network communication.
Replace the default code with the following:

local ReplicatedStorage = game:GetService("ReplicatedStorage")
local Players = game:GetService("Players")

local player = Players.LocalPlayer
local playerGui = player.PlayerGui

local IncreaseJumpPowerFunction = ReplicatedStorage.Instances.IncreaseJumpPowerFunction
local jumpPurchaseGui = ReplicatedStorage.Instances.JumpPurchaseGui
local jumpButton = jumpPurchaseGui.JumpButton

local function onButtonClicked()
	local success, purchased = pcall(IncreaseJumpPowerFunction.InvokeServer, IncreaseJumpPowerFunction)
	if not success then
		-- purchased will be the error message if success is false
		error(purchased)
	elseif success and not purchased then
		warn("Not enough coins!")
	end
end

jumpButton.Activated:Connect(onButtonClicked)

-- Add the JumpPurchaseGui to the player's Gui
jumpPurchaseGui.Parent = playerGui

Code explanation

The following sections describe the code in more detail.

Obtain references to the GUI and server function - The variables IncreaseJumpPowerFunction, jumpPurchaseGui, and jumpButton contain references to the function and GUI that calls the function that you'll need later.
Define the event handler - onButtonClicked() defines logic for when users click the upgrade button. It uses pcall() (protected call) to invoke the RemoteFunction. Any client-server communication like this requires pcall() to handle errors or connection issues.
Connect the handler to the button - The Activated event is compatible on all platforms, including mouse, touchscreen, or gamepad contexts. It triggers when a click, touch, or gamepad button is released.

Playtest

Select Test from the dropdown and click Play. The Upgrade Jump button shows up in the bottom-right corner.

Try clicking the button before you collect any coins to check that it doesn't award you additional jumping power, then try collecting some coins and see if the upgrade works when you click again.

With the code complete, try tuning the difficulty: add coins if the pace feels slow, or remove a few and tuck them in trickier spots if upgrades come too easily.