How do I get the how many days until my next birthday?

Question

I tried this but it fails

var diffDays1=(function(){ 
var oneDay = 24*60*60*1000; // hours*minutes*seconds*milliseconds
var secondDate = new Date(new Date().getFullYear()+1,4,5);
var firstDate = new Date();
 return Math.round(Math.abs((firstDate.getTime() - secondDate.getTime())/(oneDay)));
})();

Wolfram alpha says it's 330 days, diffDays1 shows it's 359. This is probably due to daylight savings or something. Is there a way to accurately calculate days since without doing it server side.

Answer 1

The problem is that you're basing the month on April being 4, when April is 3 in Javascript. See https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Date#Parameters

var diffDays1=(function(){ 
    var oneDay = 24*60*60*1000; // hours*minutes*seconds*milliseconds
    var secondDate = new Date(new Date().getFullYear()+1,3,5);
    var firstDate = new Date();
    return Math.round(Math.abs((firstDate.getTime() - secondDate.getTime())/(oneDay)));
})();