The Espruino JavaScript interpreter - Official Repo
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Espruino JavaScript for Microcontrollers

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NOTE: This software is beta and is provided as-is, and won't be considered even remotely final until we've released the Espruino Board. As such, don't expect support, and do expect it to change rapidly and without warning.


It'd probably help to read the FAQ, and specifically the page about Performance as it contains information about how Espruino itself works. There's also the auto-generated Reference for JavaScript commands.


Please see the LICENSE file


Please see

Current State

Please note that this is BETA. We've been working hard on the Espruino Board support but we haven't had time to check the other boards properly.

  • Espruino Board - working
  • Linux - working
  • HY STM32 2.4" - ?
  • HY STM32 2.8" - ?
  • HY STM32 3.2" - ?
  • Olimexino - ?
  • Carambola - ?
  • Raspberry Pi - ?
  • Sony SmartWatch - USB VCP support still needed
  • MBed platforms - have not worked for a while - hardware wrapper still needed
  • Arduino - has never worked. Compiles but doesn't even seem to get past init


If you're using Espruino for your own personal projects - go ahead, we hope you have fun - and please let us know what you do with it on!

However if you're planning on including the Espruino software in your commercial product, please read the following:

  • If you sell a board with the Espruino software on, you cannot call it 'Espruino' but you must explain clearly that it uses 'Espruino' internally (we own the trademark).
  • If you're not willing to support us, we won't support you (or your users). Please contact us about this.


We suggest that you use the CodeSourcery GCC compiler, but paths in Makefile may need changing...


  • See the top of Makefile for board names
  • Without RELEASE=1, assertions are kept in the code (which is good for debugging, bad for performance + code size)
  • BOARDNAME=1 RELEASE=1 make serialflash will flash to /dev/ttyUSB0 using the STM32 serial bootloader (what's needed for Espruino + HY boards)
  • BOARDNAME=1 RELEASE=1 make flash will flash using st-flash if discovery, or maple bootloader if using that board

Directories and Files

  • ChangeLog: What's new
  • TODO: List of things to do
  • boards/: Information on boards, used to auto-generate a lot of the code
  • code/: Example JavaScript code
  • gen/: Auto-Generated Source Files
  • libs/: Optional libraries to include in Espruino (Math, Filesystem, Graphics, etc)
  • linker/: Linker files for various processors
  • misc/: random other stuff
  • scripts/: Scripts for generating files in gen, and for analysing code/compilation/etc
  • src/: Main source code
  • targetlibs/: Libraries for targeted architectures
  • targets/: Specific code for targeted architectures
  • tests/: Testcases
  • dist_*: files to be copied into distribution zip file

Adding more devices

Currently there are a bunch of different files to modify. Eventually the plan is to fit everything into boards/ and to auto-generate the rest of the config files.

  • Most build options handled in Makefile
  • Extra libraries like USB/LCD/filesystem in Makefile
  • Linker Scripts are in linker/
  • boards/*.py files handle loading the list of available pins so the relevant headers + docs can be created
  • Processor-specific code in targets/stm32, targets/linux, etc.
  • Processor-specific libs in targetlibs/foo
  • src/jshardware.h is effectively a simple abstraction layer for SPI/I2C/etc
  • targets/stm32/jshardware.c also has flash-size-specific defines
  • libs/fat_sd and libs/lcd still have some device-specific defines in too
  • If you're low on flash, you might want to modify

Adding libraries

  • Create jswrap_mylib.c/h in libs/
  • Create library functions (see examples in other jswrap files, also the comments in scripts/

Arduino Compile (beta)

  • Ensure that targets/arduino/utility is symlinked to src
  • Symlink ...arduino_workspace/libraries/Espruino to targets/arduino

Cross Compile for Raspberry Pi

cd targetlibs
mkdir raspberrypi
cd raspberrypi
git clone git://
sudo apt-get install ia32-libs

Cross Compile for Carambola (OpenWRT)