heart rate returning null

[eclarkie22]

Hi, I am very new to javascript and am not sure what i am doing wrong here. I am having a problem where I am trying to obtain heart rate but it is returning null. I have allowed permission in the package.json files. I have simplified my code significantly just to see if I could get the value back but it is still returning null. My previous code was checking all of the necessary permissions/body presence/display on/etc. Using print statements I was able to verify that all of those worked. I have separated out the below code, and it is still returning null. What I want is to have the heart rate start when the display turns on. Do i need to add the hrm event listener? I was hoping not to need to use that, and just use the display event listener and then to grab the most recent value.

display.onaddEventListener("change", () => {
  const hrm = new HeartRateSensor();
  hrm.start();
  console.log(hrm.heartRate);
});

[Gondwana]

Try addEventListener.

Even so, that's an odd structure. You'll be starting hrm whenever the display goes on or off, and you're never stopping the hrm.

[morningReign · Accepted solution]

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@eclarkie22 wrote:

Hi, I am very new to javascript and am not sure what i am doing wrong here. I am having a problem where I am trying to obtain heart rate but it is returning null. I have allowed permission in the package.json files. I have simplified my code significantly just to see if I could get the value back but it is still returning null. My previous code was checking all of the necessary permissions/body presence/display on/etc. Using print statements I was able to verify that all of those worked. I have separated out the below code, and it is still returning null. What I want is to have the heart rate start when the display turns on. Do i need to add the hrm event listener? I was hoping not to need to use that, and just use the display event listener and then to grab the most recent value.

---

The heart rate sensor is oddly asynchronous, and you don't want to keep it actively recording if the display is off.

so,....

you can add a routine to record the heart rate:

var cHR=0;
if (HeartRateSensor) {
  const hrm = new HeartRateSensor();
  hrm.addEventListener("reading", () => {
    cHR=hrm.heartRate
  });
  display.addEventListener("change",()=>{
    if (display.on){
      hrm.start()
      cHR=hrm.heartRate
      if (typeof cHR=="number") cHRZ=user.heartRateZone(cHR)
      else cHR=0
    }else{
      hrm.stop();
    }
  });
  hrm.start();
}

 Then you can display it during your normal clock update:

clock.granularity='seconds'
clock.ontick=function (evt) {
  console.log(cHR)  
}

Regards,

Reign