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0.1.55 • Public • Published

Espruino Tools

This repository contains a set of tools for the Espruino JavaScript Interpreter.

While it is used directly by the Espruino Web IDE, there are also simple command-line and node.js interfaces.


When installed as a Node module with npm install -g espruino you get a command-line tool called espruino:

Espruino Command-line Tool 0.1.50

USAGE: espruino ...options... [file_to_upload.js]

  -h,--help                : Show this message
  -j [job.json]            : Load options from JSON job file - see configDefaults.json
                               Calling without a job filename creates a new job file
                               named after the uploaded file
  -v,--verbose             : Verbose
  -q,--quiet               : Quiet - apart from Espruino output
  -m,--minify              : Minify the code before sending it
  -t,--time                : Set Espruino's time when uploading code
  -w,--watch               : If uploading a JS file, continue to watch it for
                               changes and upload again if it does.
  -e command               : Evaluate the given expression on Espruino
                               If no file to upload is specified but you use -e,
                               Espruino will not be reset
  --sleep 10               : Sleep for the given number of seconds after uploading code
  -n                       : Do not connect to Espruino to upload code
  --board BRDNAME/BRD.json : Rather than checking on connect, use the given board name or file
  --ide [8080]             : Serve up the Espruino Web IDE on the given port. If not specified, 8080 is the default.

  -p,--port /dev/ttyX      : Connect to a serial port
  -p,--port aa:bb:cc:dd:ee : Connect to a Bluetooth device by addresses
  -p,--port tcp:// : Connect to a network device (port 23 default)
  -d deviceName            : Connect to the first device with a name containing deviceName
  --download fileName      : Download a file with the name matching fileName to the current directory
  -b baudRate              : Set the baud rate of the serial connection
                               No effect when using USB, default: 9600
  --no-ble                 : Disables Bluetooth Low Energy (using the 'noble' module)
  --remote peer-id         : Enables WebRTC connections to a phone (copy the Peer ID from
  --list                   : List all available devices and exit

  --listconfigs            : Show all available config options and exit
  --config key=value       : Set internal Espruino config option

  -o out.js                : Write the actual JS code sent to Espruino to a file
  --ohex out.hex           : Write the JS code to a hex file as if sent by E.setBootCode
  --storage fn:data.bin    : Load 'data.bin' from disk and write it to Storage as 'fn'
  --storage .boot0:-       : Store program code in the given Storage file (not .bootcde)

  -f firmware.bin[:N]      : Update Espruino's firmware to the given file
                               Must be a USB Espruino in bootloader mode
                               (bluetooth is not currently supported).
                               Optionally skip N first bytes of the bin file.

If no file, command, or firmware update is specified, this will act
as a terminal for communicating directly with Espruino. Press Ctrl-C
twice to exit.

Please report bugs via

For instance:

# Connect to Espruino and act as a terminal app  (IF Espruino is the only serial port reported)

# Connect to Espruino on the specified port, act as a terminal
espruino -p /dev/ttyACM0

# Connect to the first device found with 'Puck' in the name (eg. a Puck.js via Bluetooth)
espruino -d puck

# Write a program to Espruino (IF Espruino is the only serial port reported)
espruino myprogram.js

# Otherwise you'll want to specify the exact port first
espruino -p /dev/ttyACM0 myprogram.js

# Write a program to Espruino and drop into a terminal, but then monitor
# myprogram.js for changes and upload it again
espruino --watch myprogram.js

# Load a file into two Espruino boards
espruino -p /dev/ttyACM1 /dev/ttyACM2 mycode.js

# Load a file into Espruino and save
espruino -p /dev/ttyACM0 mycode.js -e "save()"

# Write mycode.js to the first Bangle.js device found as a Storage file named app.js
espruino -d Bangle.js mycode.js --storage app.js:-

# As above, but also write app_image.bin to the device as a Storage file named app.img
espruino -d Bangle.js mycode.js --storage app.js:- --storage app.img:app_image.bin

# Connect to Bluetooth device address c6:a8:1a:1f:87:16 and download setting.json from Storage to a local file
bin/espruino-cli.js -p c6:a8:1a:1f:87:16 --download setting.json

# Execute a single command on the default serial device
espruino -e "digitalWrite(LED1,1);"


If the NPM module noble is installed, it'll be used to scan for Bluetooth LE UART devices like Puck.js. It's an optional dependency, so will be installed if possible - but if not you just won't get BLE support.

If it is installed and you don't want it, you can use ./espruino --no-ble to disable it for the one command, or can remove the module with npm remove noble.

On linux, you'll need to run as superuser to access Bluetooth Low Energy. To avoid this you need to give node.js the relevant privileges with:

sudo setcap cap_net_raw+eip $(eval readlink -f `which node`)

Web IDE Remote Connection

It is now possible to use the CLI to connect to an Espruino device that is connected on a different computer (eg an Android phone) using the Web IDE Remote Connection (which uses WebRTC).

  • Go to on the other computer
  • Click the connect icon in the top left
  • Choose a device to connect to in order to 'pair' it
  • Take a note of the Bridge Peer ID that is displayed on the other computer
  • Enter the following on your PC, replacing ABCDEFGH with your Peer ID:
# connect via a remote device, watch myprogram.js and re-upload it if it changes
espruino --remote ABCDEFGH --watch myprogram.js

Web IDE Relay (deprecated)

It is now possible to use the CLI to connect to an Espruino device that is connected on a different computer (eg an Android phone) using the Web IDE relay.

  • Go to on the other computer
  • Click the connect icon in the top left
  • Choose a device
  • Take a note of the relay key that is displayed on the device
  • Enter the following on your PC, replacing ABCDEFGH with your relay key:
# connect via a remote device, watch myprogram.js and re-upload it if it changes
espruino --config RELAY_KEY=ABCDEFGH --watch myprogram.js

Not Connecting

Sometimes, you might want to run your JS file(s) through the Espruino Tools to create an output file that contains everything required, including modules. This file can then be sent directly to Espruino at some later time - sometimes just cat file.js > /dev/ttyACM0 is enough.

To do this, you don't need to connect, you just need to be able to specify the board type, which corresponds to a JSON file in

# Get a minified, complete JS file
espruino --board PUCKJS --minify mycode.js -o output.js

You can also request an Intel Hex style output. This only works on some devices, but allows you to write directly into Espruino's memory space with a flashing tool.

This is as if E.setBootCode(your_code) was called in the interpreter, except it doesn't have any code size limitations. It means that any functions that are defined in your program will be executed directly from Flash, without taking up any RAM.

# Get a hex file that can be flashed directly to the board (containing just the code)
espruino --board PUCKJS mycode.js --ohex output.hex

# Get a hex file, include 'myModule.js' as a file inside Storage
espruino --board PUCKJS mycode.js --storage myModule:myModule.js --ohex output.hex

# Create a complete hex file (including Espruino)
espruino --board PUCKJS mycode.js --ohex output.hex
mergehex -m espruino_2vXX_puckjs.hex output.hex -o out.hex

Note: If you're creating a complete hex file including the firmware, we do not distribute complete firmware hex files for our devices. You can either build your own from source or get in touch to request one.


In Espruino's Web IDE there are a lot of different config options. These end up toggling Config settings in Espruino. You can find what these are by going into the Web IDE, changing the option in Settings, then going to the Console window and scrolling to the bottom. You should see something like Config.RESET_BEFORE_SEND => true

You can then add the command-line option --config RESET_BEFORE_SEND=true to recreate this.

You can also use --listconfigs to give you a nice list of configs with their descriptions.

NPM Module

This is the NPM module espruino.

Once installed with npm install -g espruino it contains the following functions:

var esp = require("espruino");

/** Initialise EspruinoTools and call the callback.
 When the callback is called, the global variable 'Espruino'
 will then contain everything that's needed to use EspruinoTools */

/** Send a file to an Espruino on the given port, call the callback when done (calls 'init' automatically) */
esp.sendFile(port, filename, callback);

/** Send code to an Espruino on the given port, call the callback when done (calls 'init' automatically) */
esp.sendCode(port, "LED.set()\n", callback);

/** Execute an expression on Espruino, call the callback with the result (calls 'init' automatically) */
esp.expr(port, expr, callback(result));

/** Execute a statement on Espruino, call the callback with anything that gets printed (calls 'init' automatically) */
esp.statement(port, expr, callback(result));

/** Flash the given firmware file to an Espruino board (calls 'init' automatically) */
esp.flash(port, filename, callback);

For example, to get the current temperature of the board you can do:

require('espruino').expr('/dev/ttyACM0', 'E.getTemperature()', function(temp) {
        console.log('Current temperature is '+temp);

Note: this module is currently prints a lot of debug information to console.log when working.

If you want to set specific options, for example Baud rate, initialise everything explicitly with init, set the options, and then call the function you need:

var esp = require("espruino");
esp.init(function() {
  Espruino.Config.BAUD_RATE = "115200";
  esp.sendFile(port, filename, function() {

Job File

A job file simplifies specifying the command-line and provides a future record of the run setup. Specifying the -j option without a job file name will generate a job file automatically using the given JS code file as the base name and any commandline arguments specified.

For example, espruino -j -t -w test.js; // will create test.json

The following table provides a guide for setting configuration fields, but consult the code for certainty. Module/pluggin values generally override other keys. It is not necessary to include any fields except the ones you want.

Commandline Argument JSON Key 1,2 Module/Pluggin 2,3
file_to_upload.js file ("")
-b baudrate baudRate (0) BAUD_RATE (9600)
-c color (false)
-e command expr ("")
-f firmware.bin updateFirmware ("")
--list showDevices (false)
-m,-minify minify (false) MINIFICATION_LEVEL ("")
MINIFICATION_Mangle (true) 4
-no-ble no-ble (false) BLUETOOTH_LOW_ENERGY (true)
-o out.js outputJS ("")
-p,--port /dev/ttyX ports ([""])
-q,--quiet quiet (false)
-t,--time setTime (false) SET_TIME_ON_WRITE (false)
-v,--verbose verbose (false)
-w,--watch watchFile (false)
UI_MODE ("Normal")


  1. JSON keys equate to internal args variable keys.
  2. Default values shown in parentheses or see configDefaults.json file under node_modules/espruino folder. Check code directly for issues.
  3. Recommended for advanced users only. Module and plugin keys equate to internal Espruino.Config variable keys stored in job file as subkeys under espruino key. Consult code for possible values.
  4. Minification parameters only work if level set, e.g. MINIFICATION_LEVEL: "ESPRIMA".
  5. MODULE_URL accepts a pipe delimited (|) list of URLS, including local servers and absolute or relative paths based on the code file. For example, "../../modules|http://localhost:8080/modules|" will first look in the module folder located two folders up from the code, then query the localhost server, and then look in the Espruino repository.


This isn't well documented right now, but basically:

  • You have a bunch of source files that are automatically loaded by index.js
  • These add things to Espruino.Core or Espruino.Plugins
  • They also register themselves as processors with Espruino.addProcessor. For instance you might register for "transformForEspruino" in which case you can do something to the JS code before it's finally sent to Espruino.
  • You then call into Espruino.Core.X or Espruino.Plugins.Y to do what you want

It's not ideal for node.js, but was designed to run in the Web browser for the Espruino Web IDE


Contributions would he hugely appreciated - sadly I'm stretched a bit thin with Espruino, Espruino's modules, the Web IDE and forum, so this isn't getting the love it deserves.

Please be aware that the Espruino Web IDE (and even a truly online version of the Web IDE depend heavily this code - so try not to do anything that will break them).

Code Style

  • Please stick to a K&R style with no tabs and 2 spaces per indent
  • Filenames should start with a lowerCase letter, and different words should be capitalised, not split with underscores

Code Outline

  • Core functionality goes in core, Plugins go in plugins. See plugins/_examplePlugin.js for an example layout
  • Serial port handlers are a special case - they just add themselves to the Espruino.Core.Serial.devices array when loaded.
  • Plugins/core need to implement in init function, which is called when the document (and settings) have loaded.
  • Plugins can respond to specific events using Espruino.addProcessor. For instance you can use Espruino.addProcessor("transformForEspruino", function (data,callback) { .. }) and can modify code before it is sent to Espruino. Events types are documented at the top of espruino.js
  • Config is stored in Espruino.Config.FOO and is changed with Espruino.Config.set("FOO", value). Espruino.Core.Config.add can be used to add an option to the Settings menu.


There are other tools available to program Espruino:

Note: while other tools exist, this EspruinoTools module and the Web IDE which uses it are maintained alongside the Espruino firmware, and tend to have support for various features and edge cases that other tools might not.

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