[laukond]

I cannot make this work

local f = CreateFrame("Frame")
    f:RegisterEvent("ZONE_CHANGED")
    f:RegisterEvent("ZONE_CHANGED_NEW_AREA")
    f:RegisterEvent("PLAYER_UPDATE_RESTING")
    f:SetScript("OnEvent", function()  
    
        if IsResting() == true then
            local a, b, c, d = "UnitNameFriendlyPlayerName", "UnitNameFriendlyPetName", "UnitNameFriendlyGuardianName", "UnitNameFriendlyTotemName"
            SetCVar(a,0)
            SetCVar(b,0)
            SetCVar(c,0)
            SetCVar(d,0)
            else
            SetCVar(a,1)
            SetCVar(b,1)
            SetCVar(c,1)
            SetCVar(d,1)            
        end
    end)

Conclusion:
Little addon to hide friendly player names (not NPCs) when resting.

local cvars = {
    "UnitNameFriendlyPlayerName",
    "UnitNameFriendlyPetName",
    "UnitNameFriendlyGuardianName",
    "UnitNameFriendlyTotemName",
}
 
local f = CreateFrame("Frame")
f:RegisterEvent("PLAYER_UPDATE_RESTING")
f:SetScript("OnEvent", function()
    local value = IsResting() and 0 or 1
    for _, cvar in pairs(cvars) do
        SetCVar(cvar, value)
    end
end)