Question

12

javascript date subtraction

rated 0 times [ 14] [ 2] / answers: 1 / hits: 21886 / 15 Years ago, tue, august 18, 2009, 12:00:00

I am looking for a way to do proper subtraction between two javascript Date objects and get the day delta.

This is my approach but it fails for todays date as an input:

<script type=text/javascript>

function getDayDelta(incomingYear,incomingMonth,incomingDay){

var incomingDate = new Date(incomingYear,incomingMonth,incomingDay);

var today = new Date();



var delta = incomingDate - today;

var resultDate = new Date(delta);

return resultDate.getDate();

}

//works for the future dates:

alert(getDayDelta(2009,9,10));

alert(getDayDelta(2009,8,19));



//fails for the today as input, as expected 0 delta,instead gives 31:

alert(getDayDelta(2009,8,18));

</script>

What would be a better approach for this ?

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yosefleod

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answered 15 Years ago lesli · Accepted Answer

The month number in the Date constructor function is zero based, you should substract one, and I think that is simplier to calculate the delta using the timestamp:

function getDayDelta(incomingYear,incomingMonth,incomingDay){

  var incomingDate = new Date(incomingYear,incomingMonth-1,incomingDay),

      today = new Date(), delta;

  // EDIT: Set time portion of date to 0:00:00.000

  // to match time portion of 'incomingDate'

  today.setHours(0);

  today.setMinutes(0);

  today.setSeconds(0);

  today.setMilliseconds(0);



  // Remove the time offset of the current date

  today.setHours(0);

  today.setMinutes(0);



  delta = incomingDate - today;



  return Math.round(delta / 1000 / 60 / 60/ 24);

}





getDayDelta(2008,8,18); // -365

getDayDelta(2009,8,18); // 0

getDayDelta(2009,9,18); // 31