Save Player Position Script Donot Work?

Hello im making a game with tons of adventures and quest. I have everything i need but for some reason the save position script does not work.The script is supposed to say that is saves their position and if they rejoin game theyll be at the position they was at last.

--[[The script is supposed to say that is saves their position and if they rejoin game theyll be at the position they was at last.]]

local DataStore = game:GetService("DataStoreService"):GetDataStore("test")

game.Players.PlayerAdded:connect(function(plr)

if lastPos=nil then
    local lastPos = char.HumanoidRootPart.Position
         while true do 
         wait(1)
     DataStore:SetAsync("last",tostring(lastPos))
          end
else
game.Players.LocalPlayer.Character:MoveTo(lastPos)
end)

PLEASE HELP!