How to measure the execution time of a NodeMCU Lua function

nodemcu-execution-time.lua

-- all credits go to http://www.esp8266.com/viewtopic.php?p=64968#p64968
function profile(name)
   local start = tmr.now()
   _G[name]()
   local delta = tmr.now() - start
   print(name .. " needs " .. (delta / 1000) .. " ms")
end

function longTime()
   local sum = 0
   for i = 1, 100000, 1 do 
      sum = sum + i
   end
   print(sum)
end

profile("longTime")

-- yields:
-- > 5000050000
-- > longTime needs 474.855 ms