Help for writing an app (running zones using Karvonnen method)

Yop, I just had a few javascript classes and decided to write the app I'm waiting for :) ! Unfortunately, I have lots to learn.
I would like to implement my code as an extra feature of the run.app. It would be called run+
The missing features for which I need help are:

• to have it running in the run.app as an extra screen, accessible by swipe right/swipe left.
  
• the hr input is not tied to hrm
  
• the minimum and maximum heart rate have to be set up in the settings menu (so that other people can use it).
  

• Also, the refresh rate, for the HR (in the middle of the screen) has to be every second, but the refresh rate for the graphics could be every 4 seconds, to save memory.
  Here's the thing:

  //This app is an extra feature implementation for the Run.app of the bangle.js. It's called run+
  //I plan to have it running in the run.app, as an extra screen, accessible by swipe right/swipe left.
  //The calculation of the Heart Rate Zones is based on the Karvonnen method. It requires to know maximum and minimum heart rates. More precise calculation methods require a lab.
  //Other methods are even more approximative.
  g.clear();
  g.drawLine(44,58,88,40);
  g.drawLine(88,40,132,58);
  g.drawLine(44,116,88,134);
  g.drawLine(88,134,132,116);
  g.setFont("Vector",20);
  
  //To calculate Heart rate zones, we need to know the heart rate reserve (HRR)
  // HRR = maximum HR - Minimum HR. minhr is minimum hr, maxhr is maximum hr.
  //get the hrr (heart rate reserve).
  // I put random data here, but this has to come as a menu in the settings section so that users can change it.
  let minhr = 48;
  let maxhr = 187;
  
  function calculatehrr(minhr, maxhr) {
  return maxhr - minhr;
  }
  
  //test input for hrr (it works).
  let hrr = calculatehrr(minhr, maxhr);
  console.log(hrr);
  
  //Test input to verify the zones work. The following value for HR has to be deleted and replaced with the Heart Rate Monitor input.
  let hr = 176;
  var hr1 = hr; 
  // These variables display next and previous HR zone
  //get the hrzones right. The calculation of the Heart rate zones here is based on the Karvonnen method
  //60-70% of HRR+minHR = zone2. //70-80% of HRR+minHR = zone3. //80-90% of HRR+minHR = zone4. //90-99% of HRR+minHR = zone5. //=>99% of HRR+minHR = serious risk of heart attack
  var minzone2 = hrr * 0.6 + minhr;
  var maxzone2 = hrr * 0.7 + minhr;
  var maxzone3 = hrr * 0.8 + minhr;
  var maxzone4 = hrr * 0.9 + minhr;
  var maxzone5 = hrr * 0.99 + minhr;
  
  // HR in the middle of the screen
  g.setFont("Vector",46);
  g.drawString(hr1, 72,66);
  //these functions call background images (>6kb each) that show HRzones graphically. Flash was too memory hungry, has to be uploaded in storage.
  function getzone1() {
  return
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  }
  
  function getzone2a() {
  return
  require("heatshrink").decompress(atob("y­OR4cA///gEg8E4kEh/8HgkggEB8EHFa+27dtiVJk­mAL9lbto1C0Q1ByQCBGlIyCAQW0GomSpA0mlo1F2­2JGoinmhYyEAQXRGoxujgQyFAQXaGo5uiiw1I7dE­GpGSoA1eGQ4CCoA1JpMgGjkFGpCwGHA+QGrctGo3­QCRJuGpA0ZgJoG2gULhJuGGr9oCxykehY1E7QXQN­wqkXGorUKAA8ENwkgGqtbGomADKUCUjQ1E2jyVUg­lAGrGgXyykEGrA0WAAKkEGq1oGrCkFGt6kFpA1Ue­CgAGgSkDkAVPhY1eUgg1QwEtGr0Agg1Cj+AW50AG­r8AiQ1C/wSOpECGr8AhI1B//4JB8LGr8AGoX/8A1­NkizOACY1C/4mLGoTaBGsnwGpyhgGon/4A10/
  

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