Mini script for bayesian rule

bayescalc01.js

function bayescalc01_updateOutput_InvalidInput(invalidFieldName) {
	document.getElementById(invalidFieldName).style.backgroundColor = "lightred";
	document.getElementById('bayescalc01_pill').value = '';
	document.getElementById('bayescalc01_phealthy').value = '';
	document.getElementById('bayescalc01_ppos').value = '';
	document.getElementById('bayescalc01_pneg').value = '';
	document.getElementById('bayescalc01_correctpos').value = '';
	document.getElementById('bayescalc01_falsepos').value = '';
	document.getElementById('bayescalc01_correctneg').value = '';
	document.getElementById('bayescalc01_falseneg').value = '';
}
function bayescalc01_updateOutput() {
	if (document.getElementById('bayescalc01_prevalence') && document.getElementById('bayescalc01_sensitivity') && document.getElementById('bayescalc01_specificity')) {
		document.getElementById('bayescalc01_prevalence').style.backgroundColor = "inherit";
		document.getElementById('bayescalc01_sensitivity').style.backgroundColor = "inherit";
		document.getElementById('bayescalc01_specificity').style.backgroundColor = "inherit";

		let prevalence = document.getElementById('bayescalc01_prevalence').value;
		let sensitivity = document.getElementById('bayescalc01_sensitivity').value;
		let specificity = document.getElementById('bayescalc01_specificity').value;

		// Some sanity checking
		if(isNaN(prevalence)) { bayescalc01_updateOutput_InvalidInput('bayescalc01_prevalence'); return; }
		if(isNaN(sensitivity)) { bayescalc01_updateOutput_InvalidInput('bayescalc01_sensitivity'); return; }
		if(isNaN(specificity)) { bayescalc01_updateOutput_InvalidInput('bayescalc01_specificity'); return; }

		if((prevalence < 0) || (prevalence > 100000)) { bayescalc01_updateOutput_InvalidInput('bayescalc01_prevalence'); return; }
		if((sensitivity < 0)  || (sensitivity > 100)) { bayescalc01_updateOutput_InvalidInput('bayescalc01_sensitivity'); return; }
		if((specificity < 0) || (specificity > 100)) { bayescalc01_updateOutput_InvalidInput('bayescalc01_specificity'); return; }

		// calculation and scaling
		let psick = prevalence / 100000;
		let phealthy = 1 - psick;
		sensitivity = sensitivity / 100;
		specificity = specificity / 100;

		let ppos = psick * sensitivity + phealthy * (1 - specificity);
		let pneg = psick * (1 - sensitivity) + phealthy * specificity;

		let pcorrectpos = sensitivity * psick / ppos;
		let pfalsepos = (1 - specificity) * phealthy / ppos;
		let pcorrectneg = specificity * phealthy / pneg;
		let pfalseneg = (1 - sensitivity) * psick / pneg;

		document.getElementById('bayescalc01_pill').value = Math.round(psick * 10000) / 100;
		document.getElementById('bayescalc01_phealthy').value = Math.round(phealthy * 10000) / 100;
		document.getElementById('bayescalc01_ppos').value = Math.round(ppos * 10000) / 100;
		document.getElementById('bayescalc01_pneg').value = Math.round(pneg * 10000) / 100;

		document.getElementById('bayescalc01_correctpos').value = Math.round(pcorrectpos * 10000) / 100;
		document.getElementById('bayescalc01_falsepos').value = Math.round(pfalsepos * 10000) / 100;
		document.getElementById('bayescalc01_correctneg').value = Math.round(pcorrectneg * 10000) / 100;
		document.getElementById('bayescalc01_falseneg').value = Math.round(pfalseneg * 10000) / 100;
	}
}
document.addEventListener("DOMContentLoaded", function(event) {
	if (document.getElementById('bayescalc01_prevalence') && document.getElementById('bayescalc01_sensitivity') && document.getElementById('bayescalc01_specificity')) {
		let prevalence = document.getElementById('bayescalc01_prevalence').addEventListener('change', bayescalc01_updateOutput);
		let sensitivity = document.getElementById('bayescalc01_sensitivity').addEventListener('change', bayescalc01_updateOutput);
		let specificity = document.getElementById('bayescalc01_specificity').addEventListener('change', bayescalc01_updateOutput);
	}
});