Question

My script is returning NAN and I want it to show 0 instead.

Using || 0 has achieved this however it now returns 100 instead of 0 for var percentQ. What is causing it to return 100?

$('#observationTotalRefresh').on('click', function () {

    var 
    sumP = 0,
    sumQ = 0,
    countP = 0,
    countQ = 0;

    $('.observationPositive:not(:disabled)').each(function(){
        countP++;
        sumP += Number($(this).val());
    });
    $('.observationQuestionable:not(:disabled)').each(function(){
        countQ++;
        sumQ += Number($(this).val());
    });

    var percentP = 100/(1 + (sumQ/sumP)) || 0;
    var percentQ = (100 - percentP) || 0;

    $("#observationPositivePercentage").text(percentP.toFixed(0));
    $("#observationQuestionablePercentage").text(percentQ.toFixed(0));
    $("#observationTotal").text(sumP + sumQ);
});

Answer 1

If you do || 0 for percentP, you are ensuring that percentP is always a number. So, percentQ will always be 100 - percentP; if percentP is 0, then percentQ will be 100.

Your math for percentages seems oddly fishy, though. Perhaps you wanted

var percentP = 100 * sumP / (sumP + sumQ);

instead? Then, it’s simply

var percentP, percentQ;
if(sumP == 0 && sumQ == 0) {
    percentP = percentQ = 0;
} else {
    percentP = 100 * sumP / (sumP + sumQ);
    percentQ = 100 * sumQ / (sumP + sumQ);
}