As with flashing there are several ways to upload code from your computer to the device.

Note

The NodeMCU serial interface uses 115'200bps at boot time. To change the speed after booting, issue uart.setup(0,9600,8,0,1,1). If the device panics and resets at any time, errors will be written to the serial interface at 115'200 bps.

Tools

Transferring application code to ESP8266/8285 is an essential task, one that you'll perform quite frequently. Hence, it does make sense to try a few different uploading tools until you find one you feel comfortable with. https://frightanic.com/iot/tools-ides-nodemcu/ lists almost a dozen classical uploaders - in addition to IDEs or IDE-like applications which of course transfer code as well.

The NodeMCU firmware team does not give any recommendations as for which uploader to use nor are there any "NodeMCU approved" tools. The below listed tools are just three, in no particular order, which seem popular and/or reasonably well maintained.

ESPlorer

The essential multiplatforms tools for any ESP8266 developer from luatool author’s, including Lua for NodeMCU and MicroPython. Also, all AT commands are supported. Requires Java (Standard Edition - SE ver 7 and above) installed.

ESPlorer

Source: https://github.com/4refr0nt/ESPlorer

Supported platforms: macOS, Linux, Windows, anything that runs Java

nodemcu-uploader.py

A simple tool for uploading files to the filesystem of an ESP8266 running NodeMCU as well as some other useful commands.

Source: https://github.com/kmpm/nodemcu-uploader

Supported platforms: macOS, Linux, Windows, anything that runs Python

NodeMCU-Tool

Upload/Download Lua files to your ESP8266 module with NodeMCU firmware. Simple. Command Line. Cross-Platform. File Management. NodeMCU.

Source: https://github.com/andidittrich/NodeMCU-Tool

Supported platforms: macOS, Linux Windows, anything that runs Node.js

init.lua

You will see "lua: cannot open init.lua" printed to the serial console when the device boots after it's been freshly flashed. If NodeMCU finds a init.lua in the root of the file system it will execute it as part of the boot sequence (standard Lua feature). Hence, your application is initialized and triggered from init.lua. Usually you first set up the WiFi connection and only continue once that has been successful.

Be very careful not to lock yourself out! If there's a bug in your init.lua you may be stuck in an infinite reboot loop. It is, therefore, advisable to build a small delay into your startup sequence that would allow you to interrupt the sequence by e.g. deleting or renaming init.lua (see also FAQ). Your init.lua is most likely going to be different than the one below but it's a good starting point for customizations:

-- load credentials, 'SSID' and 'PASSWORD' declared and initialize in there
dofile("credentials.lua")

function startup()
    if file.open("init.lua") == nil then
        print("init.lua deleted or renamed")
    else
        print("Running")
        file.close("init.lua")
        -- the actual application is stored in 'application.lua'
        -- dofile("application.lua")
    end
end

-- Define WiFi station event callbacks 
wifi_connect_event = function(T) 
  print("Connection to AP("..T.SSID..") established!")
  print("Waiting for IP address...")
  if disconnect_ct ~= nil then disconnect_ct = nil end  
end

wifi_got_ip_event = function(T) 
  -- Note: Having an IP address does not mean there is internet access!
  -- Internet connectivity can be determined with net.dns.resolve().    
  print("Wifi connection is ready! IP address is: "..T.IP)
  print("Startup will resume momentarily, you have 3 seconds to abort.")
  print("Waiting...") 
  tmr.create():alarm(3000, tmr.ALARM_SINGLE, startup)
end

wifi_disconnect_event = function(T)
  if T.reason == wifi.eventmon.reason.ASSOC_LEAVE then 
    --the station has disassociated from a previously connected AP
    return 
  end
  -- total_tries: how many times the station will attempt to connect to the AP. Should consider AP reboot duration.
  local total_tries = 75
  print("\nWiFi connection to AP("..T.SSID..") has failed!")

  --There are many possible disconnect reasons, the following iterates through 
  --the list and returns the string corresponding to the disconnect reason.
  for key,val in pairs(wifi.eventmon.reason) do
    if val == T.reason then
      print("Disconnect reason: "..val.."("..key..")")
      break
    end
  end

  if disconnect_ct == nil then 
    disconnect_ct = 1 
  else
    disconnect_ct = disconnect_ct + 1 
  end
  if disconnect_ct < total_tries then 
    print("Retrying connection...(attempt "..(disconnect_ct+1).." of "..total_tries..")")
  else
    wifi.sta.disconnect()
    print("Aborting connection to AP!")
    disconnect_ct = nil  
  end
end

-- Register WiFi Station event callbacks
wifi.eventmon.register(wifi.eventmon.STA_CONNECTED, wifi_connect_event)
wifi.eventmon.register(wifi.eventmon.STA_GOT_IP, wifi_got_ip_event)
wifi.eventmon.register(wifi.eventmon.STA_DISCONNECTED, wifi_disconnect_event)

print("Connecting to WiFi access point...")
wifi.setmode(wifi.STATION)
wifi.sta.config({ssid=SSID, pwd=PASSWORD})
-- wifi.sta.connect() not necessary because config() uses auto-connect=true by default

Compiling Lua on your PC for Uploading

If you install lua on your development PC or Laptop then you can use the standard Lua compiler to syntax check any Lua source before downloading it to the ESP8266 module. However, the NodeMCU compiler output uses different data types (e.g. it supports ROMtables) so the compiled output cannot run on the ESP8266.

Compiling source on one platform for use on another (e.g. Intel x38 Window to ESP8266) is known as cross-compilation and the NodeMCU firmware supports the compilation of luac.cross on *nix patforms which have Lua 5.1, the Lua filesystem module (lfs), and the essential GCC tools. Simply change directory to the firmware root directoy and run the command:

lua tools/cross-lua.lua

This will generate a luac.cross executable in your root directory which can be used to compile and to syntax-check Lua source on the Development machine for execution under NodeMCU Lua on the ESP8266.