Am I writing this wrong or is this a bug on Date.js (date ninja)

I am trying to use datejs (date ninja or whathaveyou..) and I am getting odd results. Here's what I output to console to test.

var d1 = Date.today();
var d2 = Date.parse(work.tax_credit_start);
var span2 = new TimeSpan(d2 - d1);

console.log('result of timespan test = ' + span2.getDays() + 'days between now and ' + Date.parse(work.tax_credit_start).toString('dd-mm-yyyy') + ' - ' + work.tax_credit_start );

I am expecting about -584 days according to date开发者_开发百科 calculations in excel and other online services. Here's what I got:

result of timespan test = -462days between now and 30-00-2010 - 30-06-2010

I have got a localisation file for datejs for New Zealand style dates too, so I am not expecting that to be an issue. Though it appears to be the issue. Also if I parse a date and then render it as a string in the same format that it was in before being parsed it should not change yeah?

Long day, maybe I just need a break. Your thoughts/help internets?

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Firstly, 30-00-2010 will be resolved as Wed Dec 30 2009 00:00:00. Is that what you really want?

Secondly, the difference in days between 30-00-2010 and 30-06-2010 is only a couple of days more than 6 months, how do you get -584 days? I get -182.

Anyway, it's not a difficult calculation. Create two date objects for the required dates, set their time to noon (so as to remove daylight saving issues across dates), subtract one from the other, divide the result by the number of milliseconds in a day (24 * 60 * 60 * 1000) and round to the nearest integer.

Here's a some quick functions to do the job:

// Iput as d/m/y or d-m-y
function dmyToDate(s) {
  var bits = s.split(/[-/]/);
  return new Date(bits[2], --bits[1], bits[0]);
}


// Difference between dates in days. If only one date supplied,
// today is used for endDate
// Copy startDate so don't mess it up
function daysBetweenDates(startDate, endDate) {

  endDate = typeof endDate == 'string'? dmyToDate(endDate) : new Date();
  startDate = typeof startDate == 'string'? dmyToDate(startDate) : new Date(startDate);
  endDate.setHours(12,0,0);
  startDate.setHours(12,0,0);

  var diff = startDate - endDate;
  var ms = 24 * 60 * 60 * 1000; // or 8.64e7

  return Math.round(diff/ms);
}

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The issue is definitely caused by your work.tax_credit_start string(?) value. The Datejs parser will return a null value if parsing fails.

In your sample, d1 will be subtracted from a null Date. This will return an unexpected number value. You're then passing that 'unexpected' number into the TimeSpan constructor, which will return some unexpected .days value.

Here's a working sample of your original.

Example

var d1 = Date.parse("2010-01-30");
var d2 = Date.parse("2010-06-30");

var span2 = new TimeSpan(d2 - d1);

span2.days // 150 days

I have a couple recommendations for your original sample:

1. If you're passing a string value into Date.parse() AND you have control over the format of that value, it would be best to pass in the ISO format of yyyy-MM-dd.
2. If you're expecting a Date object returned from Date.parse(), it's best to check that value against null to ensure you actually have a valid Date object.

The following demonstrates checking for a null value of d1, then setting to a default value if null.

Example

var d1 = Date.parse("30-00-2010"); // Not a valid Date

if (!d1) {
    d1 = new Date();
}

console.log(d1); // will be 'now'

The above sample could be cleaned up by passing the default value right when setting the variable.

Example

var d1 = Date.parse("30-00-2010") || new Date();

console.log(d1); // will be 'now'

Hope this helps.