nodered_function.js

// Updated version of the very useful post: https://sixtymeters.com/automations/exporting-apple-health-data-to-home-assistant/

// preferred key names
const fieldKeyLookup = {
	qty: 'value',
	Avg: 'avg',
	Min: 'min',
	Max: 'max',
}

msg.payload = msg.payload.data.metrics.map(metric => {
	return metric.data
		.map(measurement => {
			const timestamp = Date.parse(measurement.date);
			delete measurement.date;
			var fields = {};
			Object.keys(measurement).forEach(e => {
				if (typeof(measurement[e]) !== 'object') fields[fieldKeyLookup[e] || e] = measurement[e];
			});

			if (fields.min && fields.max && fields.min == fields.max) {
				delete fields.min;
				delete fields.max;
			}

			return {
				measurement: metric.name, //active_energy
				fields: fields, // {value: 5} or {systolic:120, diastolic: 70}, etc
				tags: {
					unit: metric.units //kJ
				},
				timestamp: timestamp //2021-03-16 00:00:00 +0100
			}
		})
	})
	.flat() // we've created array for each metric consisting of array of measurements
	.filter(e => Object.keys(e.fields).length) // just in case, only return entries with fields

return msg;

note, this does not add measurements for notification metrics: irregular_heart_rate_notifications, high_heart_rate_notifications, low_heart_rate_notifications.
These consist of arrays of heartRate and/or heartRateVariation, which consist of:

• hr: 70 (or hrv: 100)
• units: bps (or: units: ms)
• timestamp: {start, interval, end}