Skip to content


Switch branches/tags


Failed to load latest commit information.
Latest commit message
Commit time

Bangle.js App Loader (and Apps)

Build Status

All software (including apps) in this repository is MIT Licensed - see LICENSE By submitting code to this repository you confirm that you are happy with it being MIT licensed, and that it is not licensed in another way that would make this impossible.

How does it work?

  • A list of apps is in apps.json (this is auto-generated from all the apps/yourapp/metadata.json using Jekyll or bin/
  • Each element references an app in apps/<id> which is uploaded
  • When it starts, BangleAppLoader checks the JSON and compares it with the files it sees in the watch's storage.
  • To upload an app, BangleAppLoader checks the files that are listed in apps.json, loads them, and sends them over Web Bluetooth.

Getting Started

Check out:

What filenames are used

Filenames in storage are limited to 28 characters. To easily distinguish between file types, we use the following:

  • is JSON that describes an app - this is auto-generated by the App Loader
  • stuff.img is an image
  • is JS code for applications
  • stuff.wid.js is JS code for widgets
  • stuff.settings.js is JS code for the settings menu
  • stuff.boot.js is JS code that automatically gets run at boot time
  • stuff.json is used for JSON settings for an app

Developing your own app

  • Head over to the Web IDE and ensure Save on Send in settings set to the default setting of To RAM
  • We'd recommend that you start off using code from 'Example Applications' (below) to get started...
  • Load app.js or widget.js into the IDE and start developing.
  • The Upload button will load your app to Bangle.js temporarily

Adding your app to the menu

  • Come up with a unique (all lowercase, no spaces) name, we'll assume myappid. Bangle.js is limited to 28 char filenames and appends a file extension (eg .js) so please try and keep filenames short to avoid overflowing the buffer.
  • Create a folder called apps/<id>, lets assume apps/myappid
  • We'd recommend that you copy files from one of the Examples in apps/_example_* (see below), or...
  • apps/myappid/app.png should be a 48px icon
  • Use to create apps/myappid/app-icon.js, using a 1 bit, 4 bit or 8 bit Web Palette "Image String"
  • Create/modify apps/myappid/metadata.json as follows:
{ "id": "myappid",
  "name": "My app's human readable name",
  "shortName" : "Short Name",
  "icon": "app.png",
  "description": "A detailed description of my great app",
  "tags": "",
  "storage": [


In the app metadata.json file you can add a list of screenshots with a line like: "screenshots" : [ { "url":"screenshot.png" } ],

To get a screenshot you can:

  • Type g.dump() in the left-hand side of the Web IDE when connected to a Bangle.js 2 - you can then right-click and save the image shown in the terminal (this only works on Bangle.js 2 - Bangle.js 1 is unable to read data back from the LCD controller).
  • Run your code in the emulator and use the screenshot button in the bottom right of the window.



This is the best way to test...

  • Fork the git repository
  • Add your files
  • Go to GitHub Settings and activate GitHub Pages
  • Run your personal Bangle App Loader at https://<your-github-username> to load apps onto your device
  • Your apps should be inside it - if there are problems, check your web browser's 'developer console' for errors

Note: It's a great idea to get a local copy of the repository on your PC, then run bin/sanitycheck.js - it'll run through a bunch of common issues that there might be.

Be aware of the delay between commits and updates on - it can take a few minutes (and a 'hard refresh' of your browser) for changes to take effect.


Using the 'Storage' icon in the Web IDE (4 discs), upload your files into the places described in your JSON:

  • app-icon.js -> myappid.img

Now load app.js up in the editor, and click the down-arrow to the bottom right of the Send to Espruino icon. Click Storage and then either choose (if you'd uploaded your app previously), or New File and then enter as the name.

Now, clicking the Send to Espruino icon will load the app directly into Espruino and will automatically run it.

When you upload code this way, your app will even be uploaded to Bangle.js's menu without you having to use the Bangle App Loader

Note: Widgets need to be run inside a clock or app, so if you're developing a widget you need to go go Settings -> Communications -> Load after saving and set it to Load default application.

Example Applications

To make the process easier we've come up with some example applications that you can use as a base when creating your own. Just come up with a unique name (ideally lowercase, under 20 chars), copy apps/_example_app or apps/_example_widget to apps/myappid, and edit apps/myappid/metadata.json accordingly.

Note: the max filename length is 28 chars, so we suggest an app ID of under 20 so that when .app.js/etc gets added to the end the filename isn't cropped.

If you're making a widget please start the name with wid to make it easy to find!

App Example

The app example is available in apps/_example_app

Apps are listed in the Bangle.js menu, accessible from a clock app via the middle button.

  • metadata.json - describes the app to bootloader and loader
  • app.png - app icon - 48x48px
  • app-icon.js - JS version of the icon (made with for use in Bangle.js's menu
  • app.js - app code
  • ChangeLog - A file containing a list of changes to your app so users can see what's changed


The icon image and short description is used in Bangle.js's launcher.

Use the Espruino image converter and upload your app.png file.

Follow this steps to create a readable icon as image string.

  1. upload a 48x48 png file - THE IMAGE SHOULD BE 48x48 OR LESS
  2. set X Use Compression
  3. set X Transparency (optional)
  4. set Diffusion: flat
  5. set Colours: 1 bit, any of the Optimised options, or 8 bit Web Palette are best
  6. set Output as: Image String

Replace this line with the image converter output:


Do not add a trailing semicolon

You can also use this converter for creating images you like to draw with g.drawImage() with your app.

Apps that need widgets can call Bangle.loadWidgets() once at startup to load them, and then Bangle.drawWidgets() to draw them onto the screen whenever the app has call to completely clear the screen. Widgets themselves will update as and when needed.

Widget Example

The widget example is available in apps/_example_widget

  • metadata.json - describes the widget to bootloader and loader
  • widget.js - widget code

Widgets are just small bits of code that run whenever an app that supports them calls Bangle.loadWidgets(). If they want to display something in the 24px high widget bar at the top of the screen they can add themselves to the global WIDGETS array with:

  area:"tl", // tl (top left), tr (top right), bl (bottom left), br (bottom right)
  sortorder:0, // (Optional) determines order of widgets in the same corner
  width: 24, // how wide is the widget? You can change this and call Bangle.drawWidgets() to re-layout
  draw:draw // called to draw the widget

When the widget is to be drawn, x and y values are set up in WIDGETS["mywidget"] and draw can then use this.x and this.y to figure out where it needs to draw to.


This is a file containing a list of changes to your app so users can see what's changed, for example:

0.01: New App!
0.02: Changed the colors
0.03: Made the app run quicker

Entries should be newest last, with the version number of the last entry matching the version in metadata.json

Please keep the same format at the example as the file needs to be parsed by the BangleApps tools. format

This is the file that's auto-generated from metadata.json and loaded onto Bangle.js by the App Loader, and which gives information about the app for the Launcher.

  "name":"Short Name", // for Bangle.js menu
  "icon":"*myappid", // for Bangle.js menu
  "src":"-myappid", // source file
  "type":"widget/clock/app/bootloader/...", // optional, default "app"
     // see 'type' in 'metadata.json format' below for more options/info
     // added by BangleApps loader on upload based on metadata.json
     // added by BangleApps loader on upload - lists all files
     // that belong to the app so it can be deleted
     // added by BangleApps loader on upload - lists files that
     // the app might write, so they can be deleted on uninstall
     // typically these files are not uploaded, but created by the app
     // these can include '*' or '?' wildcards

metadata.json format

{ "id": "appid",              // 7 character app id
  "name": "Readable name",    // readable name
  "shortName": "Short name",  // short name for launcher
  "version": "0v01",          // the version of this app
  "description": "...",       // long description (can contain markdown)
  "icon": "icon.png",         // icon in apps/
  "screenshots" : [ { "url":"screenshot.png" } ], // optional screenshot for app
  "type":"...",               // optional(if app) -  
                              //   'app' - an application
                              //   'clock' - a clock - required for clocks to automatically start
                              //   'widget' - a widget
                              //   'bootloader' - an app that at startup (app.boot.js) but doesn't have a launcher entry for 'app.js'
                              //   'settings' - apps that appear in Settings->Apps (with appname.settings.js) but that have no 'app.js'
                              //   'RAM' - code that runs and doesn't upload anything to storage
                              //   'launch' - replacement 'Launcher'
                              //   'textinput' - provides a 'textinput' library that allows text to be input on the Bangle
                              //   'scheduler' - provides 'sched' library and boot code for scheduling alarms/timers
                              //                 (currently only 'sched' app)
                              //   'notify' - provides 'notify' library for showing notifications
                              //   'locale' - provides 'locale' library for language-specific date/distance/etc
                              //              (a version of 'locale' is included in the firmware)
  "tags": "",                 // comma separated tag list for searching
  "supports": ["BANGLEJS2"],  // List of device IDs supported, either BANGLEJS or BANGLEJS2
  "dependencies" : { "notify":"type" } // optional, app 'types' we depend on (see "type" above)
  "dependencies" : { "messages":"app" } // optional, depend on a specific app ID
                              // for instance this will use notify/notifyfs is they exist, or will pull in 'notify'
  "readme": "",      // if supplied, a link to a markdown-style text file
                              // that contains more information about this app (usage, etc)
                              // A 'Read more...' link will be added under the app

  "custom": "custom.html",    // if supplied, apps/custom.html is loaded in an
                              // iframe, and it must post back an 'app' structure
                              // like this one with 'storage','name' and 'id' set up
                              // see below for more info

  "customConnect": true,      // if supplied, ensure we are connected to a device
                              // before the "custom.html" iframe is loaded. An
                              // onInit function in "custom.html" is then called
                              // with info on the currently connected device.                 

  "interface": "interface.html",   // if supplied, apps/interface.html is loaded in an
                              // iframe, and it may interact with the connected Bangle
                              // to retrieve information from it
                              // see below for more info

  "allow_emulator":true,      // if 'app.js' will run in the emulator, set to true to
                              // add an icon to allow your app to be tested

  "storage": [                // list of files to add to storage
    {"name":"appid.js",       // filename to use in storage.
                              // If name=='RAM', the code is sent directly to Bangle.js and is not saved to a file
     "url":"",                // URL of file to load (currently relative to apps/)
     "content":"...",         // if supplied, this content is loaded directly
     "evaluate":true,         // if supplied, data isn't quoted into a String before upload
                              // (eg it's evaluated as JS)
     "noOverwrite":true       // if supplied, this file will not be overwritten if it
                              // already exists
     "supports": ["BANGLEJS2"]// if supplied, this file will ONLY be uploaded to the device
                              // types named in the array. This allows different versions of
                              // the app to be uploaded for different platforms
  "data": [                   // list of files the app writes to
    {"name":"",  // filename used in storage
     "storageFile":true       // if supplied, file is treated as storageFile
     "url":"",                // if supplied URL of file to load (currently relative to apps/)
     "content":"...",         // if supplied, this content is loaded directly     
     "evaluate":true,         // if supplied, data isn't quoted into a String before upload
                              // (eg it's evaluated as JS)     
    {"wildcard":"*" // wildcard of filenames used in storage
    },                         // this is mutually exclusive with using "name"
  "sortorder" : 0,            // optional - choose where in the list this goes.
                              // this should only really be used to put system
                              // stuff at the top
  • name, icon and description present the app in the app loader.
  • tags is used for grouping apps in the library, separate multiple entries by comma. Known tags are tool, system, clock, game, sound, gps, widget, launcher or empty.
  • storage is used to identify the app files and how to handle them
  • data is used to clean up files when the app is uninstalled

metadata.json: custom element

Apps that can be customised need to define a custom element in metadata.json, which names an HTML file in that app's folder.

When custom is defined, the 'upload' button is replaced by a customize button, and when clicked it opens the HTML page specified in an iframe.

In that HTML file you're then responsible for handling a button press and calling sendCustomizedApp with your own customised version of what's in metadata.json:

    <link rel="stylesheet" href="../../css/spectre.min.css">
    <p><button id="upload" class="btn btn-primary">Upload</button></p>
    <script src="../../lib/customize.js"></script>
      document.getElementById("upload").addEventListener("click", function() {
          id : "myappid",
            {name:"", url:"app.js", content:app_source_code},
            {name:"myappid.img", content:'require("heatshrink").decompress(atob("mEwg...4"))', evaluate:true},

This'll then be loaded in to the watch. See [apps/qrcode/grcode.html](the QR Code app) for a clean example.

Note: we specify a url for JS files even though it doesn't have to exist and will never be loaded. This is so the app loader can tell if it's a JavaScript file based on the extension, and if so it can minify and pretokenise it.

metadata.json: interface element

Apps that create data that can be read back can define a interface element in metadata.json, which names an HTML file in that app's folder.

When interface is defined, a Download from App button is added to the app's description, and when clicked it opens the HTML page specified in an iframe.

    <link rel="stylesheet" href="../../css/spectre.min.css">
    <script src="../../lib/interface.js"></script>
    <div id="t">Loading...</div>
      function onInit() {
        Puck.eval("E.getTemperature()", temp=> {
          document.getElementById("t").innerHTML = temp;

When the page is ready a function called onInit is called, and in that you can call Puck.write and Puck.eval to get the data you require from Bangle.js.

See [apps/gpsrec/interface.html](the GPS Recorder) for a full example.

Adding configuration to the "Settings" menu

Apps (or widgets) can add their own settings to the "Settings" menu under "App/widget settings".
To do so, the app needs to include a settings.js file, containing a single function that handles configuring the app.
When the app settings are opened, this function is called with one argument, back: a callback to return to the settings menu.

Usually it will save any information in myappid.json where myappid is the name of your app - so you should change the example accordingly.

Example settings.js

// make sure to enclose the function in parentheses
(function(back) {
  let settings = require('Storage').readJSON('myappid.json',1)||{};
  if (typeof settings.monkeys !== "number") settings.monkeys = 12; // default value
  function save(key, value) {
    settings[key] = value;
    require('Storage').write('myappid.json', settings);
  const appMenu = {
    '': {'title': 'App Settings'},
    '< Back': back,
    'Monkeys': {
      value: settings.monkeys,
      onchange: (m) => {save('monkeys', m)}

In this example the app needs to add myappid.settings.js to storage in metadata.json.
It should also add myappid.json to data, to make sure it is cleaned up when the app is uninstalled.

  { "id": "myappid",
    "storage": [
    "data": [


You can include any of Espruino's modules as normal with require("modulename"). If you want to develop your own module for your app(s) then you can do that too. Just add the module into the modules folder then you can use it from your app as normal.

You won't be able to develop apps using your own modules with the IDE, so instead we'd recommend you write your module to a Storage File called modulename on Bangle.js. You can then develop your app as normal on Bangle.js from the IDE.

Coding hints

  • use g.setFont(.., size) to multiply the font size, eg ("6x8",3) : "18x24"

  • use g.drawString(text,x,y,true) to draw with background color to overwrite existing text

  • use g.clearRect() to clear parts of the screen, instead of using g.clear()

  • use g.fillPoly() or g.drawImage() for complex graphic elements

  • using g.clear() can cause screen flicker

  • using g.setLCDBrightness() can save you power during long periods with lcd on

  • chaining graphics methods, eg g.setColor(0xFD20).setFontAlign(0,0).setfont("6x8",3)

Misc Notes

  • Need to save state? Use the E.on('kill',...) event to save JSON to a file called myappid.json, then load it at startup.

  • 'Alarm' apps define a file called alarm.js which handles the actual alarm window.

  • Locale is handled by require("locale"). An app may create a locale file in Storage which is a module that overwrites Bangle.js's default locale.

Graphic areas

The screen is parted in a widget and app area for lcd mode direct(default).

areas as rectangle or point
Widget (0,0,239,23)
Apps (0,24,239,239)
BTN1 (230, 55)
BTN2 (230, 140)
BTN3 (230, 210)
BTN4 (0,0,119, 239)
BTN5 (120,0,239,239)
  • Use g.setFontAlign(0, 0, 3) to draw rotated string to BTN1-BTN3 with g.drawString().

  • For BTN4-5 the touch area is named

Available colors

You can use g.setColor(r,g,b) OR g.setColor(16bitnumber) - some common 16 bit colors are below:

color-name color-value
Black 0x0000
Navy 0x000F
DarkGreen 0x03E0
DarkCyan 0x03EF
Maroon 0x7800
Purple 0x780F
Olive 0x7BE0
LightGray 0xC618
DarkGrey 0x7BEF
Blue 0x001F
Green 0x07E0
Cyan 0x07FF
RED 0xF800
Magenta 0xF81F
Yellow 0xFFE0
White 0xFFFF
Orange 0xFD20
GreenYellow 0xAFE5
Pink 0xF81F

API Reference


Bangle Class

Graphics Class

'Testing' folder

The testing folder contains snippets of code that might be useful for your apps.

  • testing/colors.js - 16 bit colors as name value pairs
  • testing/gpstrack.js - code to store a GPS track in Bangle.js storage and output it back to the console


The majority of icons used for these apps are from Icons8 - we have a commercial license but icons are also free for Open Source projects.


Bangle.js App Loader (and Apps)







No releases published


No packages published