function calcPassedPercentageInThisYear(date) {
    var thisNewYear = new Date(date.getFullYear() + "/1/1");
    var nextNewYear = new Date((date.getFullYear()+1) + "/1/1");
    return 1 - (nextNewYear - date) / (nextNewYear - thisNewYear);
}

var date = new Date();
var passedPercentageInThisYear = Math.round(calcPassedPercentageInThisYear(date) * 10000.0) / 100.0;
console.log(passedPercentageInThisYear + " percent has passed in this year!");