Add a javascript version of the prediction example.

docs/README_concept2_predictions.md

@@ -1,6 +1,9 @@
 #  Wattage predictions
 
-See [concept2_predictions.py](concept2_predictions.py)
+See:
+
+* [concept2_predictions.py](concept2_predictions.py)
+* [concept2_predictions.js](concept2_predictions.js)
 
 ## Zones
 
@@ -49,4 +52,3 @@ UT2 power range is 15% (60% minus 45%)
 so 132 bmp should be 4 fifths into that 15% = 12%
 
 so expected power is 110W/(45%+12%) = 193W
-

docs/concept2_prediction.js

@@ -0,0 +1,63 @@
+function calculateWattage(restingHeartRate, maximumHeartRate, heartRate, basePowerOutput) {
+    function getZonePercentile(heartRate, restingHeartRate, maximumHeartRate) {
+        const HRR = maximumHeartRate - restingHeartRate;
+        const zonePercentage = ((heartRate - restingHeartRate) / HRR) * 100;
+        return Math.round(zonePercentage * 100) / 100;
+    }
+
+    function getHrrRange(zone) {
+        if (zone <= 65) return [0, 65];
+        else if (zone <= 70) return [65, 70];
+        else if (zone <= 80) return [70, 80];
+        else if (zone <= 85) return [80, 85];
+        else if (zone <= 95) return [85, 95];
+        else return [95, 100];
+    }
+
+    function getPowerRange(zone) {
+        if (zone <= 65) return [0, 45];
+        else if (zone <= 70) return [45, 60];
+        else if (zone <= 80) return [60, 70];
+        else if (zone <= 85) return [70, 80];
+        else if (zone <= 95) return [80, 105];
+        else return [105, 115];
+    }
+
+    const zonePercentage = getZonePercentile(heartRate, restingHeartRate, maximumHeartRate);
+    console.log("Zone:", zonePercentage);
+
+    const minPower = getPowerRange(zonePercentage)[0];
+    const maxPower = getPowerRange(zonePercentage)[1];
+
+    const [minHrr, maxHrr] = getHrrRange(zonePercentage);
+    console.log("Min HRR:", minHrr);
+    console.log("Max HRR:", maxHrr);
+
+    const powerRange = maxPower - minPower;
+    console.log("Power range:", powerRange);
+
+    const hrrRange = maxHrr - minHrr;
+    console.log("HRR range:", hrrRange);
+    console.log("Zone minus min HRR:", zonePercentage - minHrr);
+
+    const hrrPercentage = (zonePercentage - minHrr) / hrrRange;
+    console.log("HRR percentage:", hrrPercentage);
+
+    const powerPercentage = (minPower + hrrPercentage * powerRange) / 100;
+    console.log("Power percentage:", powerPercentage);
+
+    // Calculate predicted power
+    const predictedPower = basePowerOutput / powerPercentage;
+
+    return Math.round(predictedPower);
+}
+
+// Example usage
+const restingHeartRate = 58;
+const maximumHeartRate = 165;
+const heartRate = 132;
+const basePowerOutput = 110;
+
+const watts = calculateWattage(restingHeartRate, maximumHeartRate, heartRate, basePowerOutput);
+console.log(`Predicted power: ${watts} watts`);
+