_try.lua

local tooltip
local function create_tooltip()
  local tip, fontstrings = CreateFrame("GameTooltip", "temptt"), {}
  for i = 1, 8 do
    local L,R = tip:CreateFontString(), tip:CreateFontString()
    L:SetFontObject(GameFontNormal)
    R:SetFontObject(GameFontNormal)
    tip:AddFontStrings(L,R)
    table.insert(fontstrings,L)
    table.insert(fontstrings,R)
  end
  tip.fontstrings = fontstrings
  return tip
end
local function is_soulbound_item(bag, slot)   -- returns boolean
  tooltip = tooltip or create_tooltip()
  tooltip:SetHyperlink('item:')
  tooltip:SetOwner(UIParent,"ANCHOR_NONE")
  tooltip:SetBagItem(bag, slot)
  for i,v in ipairs(tooltip.fontstrings) do
    if v:GetText() == ITEM_SOULBOUND then
      return true
    end
  end
  return false
end


local itemId = GetContainerItemID(0, 1)
print("HS: "..itemId) -- Hearthstone is at 0,1

local soulbound = is_soulbound_item(0, 1)
if soulbound then
   print("Soulbound")
end