Simple DataStore script keeps returning an error?

My DataStore script isn't working it keep getting an error saying that GetAsync() is not a valid member of datastore?

local datastore = game:GetService("DataStoreService")
game.Players.PlayerAdded:connect(function(player)
    local leaderstats = Instance.new("IntValue")
    leaderstats.Name = "Stat"
    leaderstats.Parent = player
    local stata = Instance.new("BoolValue")
    stata.Name = "NewPlayer"
    stata.Parent = leaderstats
    local key = "user-" .. player.userId
    local storeditems = datastore:GetAsync(key)
    if storeditems then
        stata.Value = storeditems[1]
    else
        local items = {stata.Value}
        datastore:SetAsync(key, items)
    end
end)
game.Players.PlayerRemoving:connect(function(player)
    local items = {player.Leaderstats.Stat.Value}
    local key = "user-" .. player.userId
    datastore:SetAsync(key, items)
end)