WoW Lua error; attempt to call a global(a nil value)

Question

I'm new to Lua and was following the tutorial on https://wowwiki.fandom.com/wiki/AddOn_tutorial but i just cant get it to work; i have copied the code but i get the error message " attempt to call a global 'functionname' (a nil value) " on both the SetMapToCurrentZone() and the GetPlayerMapPosition("player") functions.

This is the entire Lua file;

local zone = nil
local TimeSinceLastUpdate = 0
 local function UpdateCoordinates(self, elapsed)
    if zone ~= GetRealZoneText() then
    zone = GetRealZoneText()
    SetMapToCurrentZone()
    end
     TimeSinceLastUpdate = TimeSinceLastUpdate + elapsed
    if TimeSinceLastUpdate > .5 then    
            TimeSinceLastUpdate = 0
        local posX, posY = GetPlayerMapPosition("player");      
        local x = math.floor(posX * 10000)/100
        local y = math.floor(posY*10000)/100
        eCoordinatesFontString:SetText("|c98FB98ff("..x..", "..y..")")  
    end 
end
 
function eCoordinates_OnLoad(self, event,...) 
    self:RegisterEvent("ADDON_LOADED")  
end
 function eCoordinates_OnEvent(self, event, ...) 
     if event == "ADDON_LOADED" and ... == "eCoordinates" then
        self:UnregisterEvent("ADDON_LOADED")        
        eCoordinates:SetSize(100, 50)
            eCoordinates:SetPoint("TOP", "Minimap", "BOTTOM", 5, -5)
            eCoordinates:SetScript("OnUpdate", UpdateCoordinates)
        local coordsFont =    eCoordinates:CreateFontString("eCoordinatesFontString", "ARTWORK", "GameFontNormal")
        coordsFont:SetPoint("CENTER", "eCoordinates", "CENTER", 0, 0)
        coordsFont:Show()
        eCoordinates:Show()     
    end
end

How do i fix it?

Answer 1

These functions have been renamed and moved to a wrapper object in 8.0, to C_Map.GetBestMapForUnit (requiring "player" as parameter to yield the same result) and C_Map.GetPlayerMapPosition respectively.

You can probably expect more functions that are called later to throw the same error, their lines just couldn't be reached before. I can check the whole code example when I'm at a desktop again, but you may simply look up these functions on Wowpedia , especially other map-related functions.
I suggest using Wowpedia over Wowwiki, it's a personal preference/impression, the former seems to receive more constant updates. (The two seem to be merging again now, after splitting 10 years ago)