GATT flow

hr-service-2.ts

import { Injectable } from '@angular/core';
import { Observable } from 'rxjs/Observable';
import { BluetoothCore } from '@manekinekko/angular-web-bluetooth';


@Injectable()
export class HeartRateService {

  static GATT_CHARACTERISTIC_HR_MEASUREMENT = 'heart_rate_measurement';
  static GATT_PRIMARY_SERVICE = 'heart_rate';

  constructor(
    public ble: BluetoothCore
  ) {}
  ...
}

hr-service.ts

public getHeartRate() {
  try {
      return this.ble
        .discover$({
          acceptAllDevices: true,
          optionalServices: [HeartRateService.GATT_PRIMARY_SERVICE],
        } as RequestDeviceOptions)
        .mergeMap( (gatt: BluetoothRemoteGATTServer)  => {
          return this.ble.getPrimaryService$(gatt, HeartRateService.GATT_PRIMARY_SERVICE);
        })
        .mergeMap( (primaryService: BluetoothRemoteGATTService) => {
          return this.ble.getCharacteristic$(primaryService, HeartRateService.GATT_CHARACTERISTIC_HR_MEASUREMENT);
        })
        .mergeMap( (characteristic: BluetoothRemoteGATTCharacteristic) =>  {
          return this.ble.readValue$(characteristic);
        })
        .map( (value: DataView) => {
          return this.parseHeartRate(value);
        });
  } catch (e) {
    console.error('Oops! can not read value from %s');
  }
}