setElementSpeed

[golanu21]

addCommandHandler("setmyspeed", 
function (player, cmd, arg1) 
  local veh = getPedOccupiedVehicle(player) 
  if (veh) then 
    setElementSpeed(veh, "kph", tonumber(arg1)) 
  else 
    outputChatBox("You have to sit in vehicle", player) 
  end 
end 
) 

the code is from www.wiki.multitheftauto.com

server.lua:5: attempt to call global 'setElementSpeed' (a nil value) 

[EstrategiaGTA]

Because it isn't a function. It's an useful function. And as I can see HERE, you also need the useful function 'getElementSpeed'.

[qaisjp]

As an extension to EstrategiaGTA's post, all content in Useful functions are snippets that you need to include into your resource before calling them. You found this example from a Useful function example, so naturally you need that function.