Roll20 API script for automatically marking tokens as bloodied or dead

dead_and_bloodied.js

/**
 * dead_and_bloodied.js v1.0
 * Duane Sibilly <[email protected]>
 * 
 * Description: Listens for token bar changes to identify when tokens are
 * bloodied (reduced to half HP or less) and dead (reduced to 0 HP or less.)
 */
on('ready', () => {
	const barNumber = 1, // Set this to the bar you're using for HP: 1, 2, or 3
		barObject = { // This represents the bar as an abstract object
			value: 0.0,
			max: 0.0,
			// Some convenience methods to perform bloodied & death calculations
			isBloodied: function () {
				return this.value <= this.max / 2 && this.value > 0;
			},
			isDead: function () {
				return this.value <= 0;
			},
		},
		bloodied = 'red', // Set this to the id of the token marker representing bloodied
		dead = 'dead', // Set this to the id of the token marker representing dead
		scriptName = 'dead_and_bloodied.js',
		
		// unpacks the status marker string into an object
		unpackStatusMarkers = stats => stats.split(/,/).reduce((statusObject, value) => {
			let statusName = value.split(/@/),
				statusNumber;
			
			statusName[0] = statusName[0].toLowerCase();
			statusNumber = parseInt(statusName[1] || '0', 10);
			if (statusName[0].length) {
				statusObject[statusName[0]] = Math.max(statusNumber, statusObject[statusName[0]] || 0);
			}
			
			return statusObject;
		}, {}),
		// serializes a status marker object into a comma-delimited string
		packStatusMarkers = statusObject => Object.keys(statusObject).map(status => {
			if (status === 'dead' || statusObject[status] === true || statusObject[status] < 1 || statusObject[status] > 9) {
				// If the status is a name, a Boolean, or outside the bounds [1, 9], do nothing
				return status;
			}
			
			// If the status is a Number, turn it into name@number
			return `${status}@${parseInt(statusObject[status], 10)}`;
		}).join(','),
		// handler callback for bar changes
		barChangeHandler = tokenObject => {
			const statusMarkers = unpackStatusMarkers(tokenObject.get('statusmarkers'));
			
			barObject.value = parseFloat(tokenObject.get(`bar${barNumber}_value`));
			barObject.max = parseFloat(tokenObject.get(`bar${barNumber}_max`));
			
			if (Number.isNaN(barObject.max)) {
				// If the bar has no max set, do nothing
				return;
			}
			
			// Update bloodied status
			if (barObject.isBloodied()) {
				statusMarkers[bloodied] = true;
			} else {
				delete statusMarkers[bloodied];
			}
			
			// Update dead status 
			if (barObject.isDead()) {
				statusMarkers[dead] = true;
			} else {
				delete statusMarkers[dead];
			}
			
			// Serialize and save status changes to the token
			tokenObject.set({
				statusmarkers: packStatusMarkers(statusMarkers)
			});
		};
	
	// When the selected bar changes, fire off the handler callback!
	on(`change:graphic:bar${barNumber}_value`, barChangeHandler);
});