A sample BLE peripheral service and characteristic for use with Node.js and bleno.

characteristic.js

/*  characteristic.js 
 *  A simple custom BLE peripheral characteristic for use with Node.js and bleno.
 *  This characteristic supports read, write, and notify properties.
 *  Julian Hays - 10/14/19
 */

var util = require('util');
var bleno = require('bleno-mac'); //or 'bleno-mac' if you are using that
var BlenoCharacteristic = bleno.Characteristic;

var CustomCharacteristic = function() {
	CustomCharacteristic.super_.call(this, {
		uuid: 'fd758b93-0bfa-4c52-8af0-85845a74a606',
		properties: ['read', 'write', 'notify']
	});

	this._value = new Buffer(0);
	this._updateValueCallback = null;
};

util.inherits(CustomCharacteristic, BlenoCharacteristic);
module.exports = CustomCharacteristic;

CustomCharacteristic.prototype.onReadRequest = function (offset, callback) {
	console.log('CustomCharacteristic onReadRequest');
	var data = new Buffer(1);
	data.writeUInt8(42, 0);
	callback(this.RESULT_SUCCESS, data);
};

CustomCharacteristic.prototype.onWriteRequest = function(data, offset, withoutResponse, callback) {
	this._value = data;
	console.log('CustomCharacteristic - onWriteRequest: value = ' + this._value.toString('hex'));
	callback(this.RESULT_SUCCESS);
};

var isSubscribed = false
var notifyInterval = 5 //seconds

function delayedNotification(callback) {
	setTimeout(function() { 
		if (isSubscribed) {
			var data = Buffer(3);
			var now = new Date();
			data.writeUInt8(now.getHours(), 0);
			data.writeUInt8(now.getMinutes(), 1);
			data.writeUInt8(now.getSeconds(), 2);
			callback(data);
			delayedNotification(callback);
		}
	}, notifyInterval * 1000);
}

CustomCharacteristic.prototype.onSubscribe = function(maxValueSize, updateValueCallback) {
	console.log('CustomCharacteristic - onSubscribe');
	isSubscribed = true;
	delayedNotification(updateValueCallback);
	this._updateValueCallback = updateValueCallback;
};

CustomCharacteristic.prototype.onUnsubscribe = function() {
	console.log('CustomCharacteristic - onUnsubscribe');
	isSubscribed = false;
	this._updateValueCallback = null;
};

service.js

/*  service.js 
 *  A simple custom BLE peripheral service for use with Node.js and bleno.
 *  Julian Hays - 10/14/19
 */

var bleno = require('bleno-mac') ; 
var BlenoPrimaryService = bleno.PrimaryService;

bleno.on('stateChange', function(state) {
console.log('on -> stateChange: ' + state);
	if (state === 'poweredOn') {
		console.log("request startAdvertising");
		bleno.startAdvertising('CustomService', ['27cf08c1-076a-41af-becd-02ed6f6109b9']);  
	} else {
		console.log("request stopAdvertising");
		bleno.stopAdvertising(); 
	}
});

var CustomCharacteristic = require('./characteristic');

bleno.on('advertisingStart', function(error) {
	console.log('on -> advertisingStart: ' + (error ? 'error ' + error : 'success'));

	if (!error) {
		bleno.setServices([
			new BlenoPrimaryService({
				uuid: '27cf08c1-076a-41af-becd-02ed6f6109b9',
				characteristics: [
					new CustomCharacteristic()
				]
			})
		]);
	}
});

I tried on Windows 7.
npm install bluetooth-hci-socket fails with some error messages. Have no access to the log right now. Maybe tomorrow.

But I am about to give up on mocking a BLE device on Windows now. Found a way with my own code to mock it on Android.

But thanks for the quick reply.

Glad you found another solution. If you give it another try on Windows, perhaps this thread will help:

noble/node-bluetooth-hci-socket#35

hey
unable to run on catalina.
stateChange event doesn't call.
and it stuck at bleno-echo example .

To run on a newer macOS you need bleno-mac and some specific package branches.

Try this on your package.json

  "dependencies": {
    "bleno": "github:notjosh/bleno#inject-bindings",
    "bleno-mac": "github:notjosh/bleno-mac",
    "xpc-connection": "sandeepmistry/node-xpc-connection#pull/26/head"
  },
  "resolutions": {
    "xpc-connection": "sandeepmistry/node-xpc-connection#pull/26/head"
  }

Then import bleno-mac as bleno

Thanks for sharing the code and guide link.
Your code and step-by-step guide is very well explained.

A step-by-step tutorial on this code is available on the Punch Through blog:
https://punchthrough.com/how-to-use-node-js-to-speed-up-ble-app-development/

How can we show multiple characteristics? Adding new is not working (see below code example)

characteristics: [ new CustomCharacteristic(), new NewCustomCharacteristic(), // Add new here ]

help me to add multiple services and/or characteristics.