inventory system example (Roblox)

local inventory = {}

local function addItems(player, itemName)
    if type(inventory[player]) == "table" then
        inventory[player][#inventory[player]+1] = itemName
    else
        inventory[player] = {}
        inventory[player][#inventory[player]+1] = itemName
    end
end

local function removeItems(player, itemName)
    if type(inventory[player]) == "table" then
        for k,v in pairs(inventory[player]) do
            if v == itemName then
                inventory[player][k] = nil -- if this doesnt work, do:
                -- inventory[player][itemName] = nil
                break
            end
        end
    end
end

local DS = game:GetService("DataStoreService")
local inventoryStore = DS:GetDataStore("Inventories")

local function loadInventory(player)
    if player.UserId < 1 then return end -- dont load or save for guests.
    local success, loaded = pcall(function()
        local didLoad = false
        local getId = tonumber(player.UserId) or 0
        inventoryStore:UpdateAsync("user-"..getId,function(storedData)
            local manageData = storedData or {}
            inventory[player] = manageData
            didLoad = true
            return manageData
        end)
        return didLoad
    end)
    if success and loaded then
        print("Successfully loaded inventory for: "..tostring(player))
    else
        warn("Error loading inventory for: "..tostring(player))
    end
end

local function saveInventory(player)
    if player.UserId < 1 then return end -- dont load or save for guests.
    local success, saved = pcall(function()
        local didSave = false
        local getId = tonumber(player.UserId) or 0
        inventoryStore:UpdateAsync("user-"..getId,function(storedData)
            local manageData = storedData or {}
            manageData = inventory[player]
            didSave = true
            return manageData
        end)
        return didSave
    end)
    if success and saved then
        print("Successfully saved inventory for: "..tostring(player))
    else
        warn("Error saving inventory for: "..tostring(player))
    end
end

local itemStorage = game.ServerStorage.DataType

local function applyInventory(player)
    if type(inventory[player]) == "table" then
        for k,v in pairs(inventory[player]) do
            if itemStorage:FindFirstChild(v) then
                itemStorage[v]:Clone().Parent = player.Backpack
            end
        end
    end
end

game.Players.PlayerAdded:Connect(function(player)
    inventory[player] = {}
    loadInventory(player)
    applyInventory(player)
end)

game.Players.PlayerRemoving:Connect(function(player)
    saveInventory(player)
end)