days from an event

[Vegan]

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var oldevent = new date(2012, 7, 2);
var today = new date;
document.write(today-oldevent);

I am expecting days so any problems with this approach?

[califdon]

Take a look at http://www.adp-gmbh.ch/web/js/date/add_days.html

Oops, this one is closer to what you want to do: http://www.javascriptkit.com/javatutors ... ence.shtml

Unlike Microsoft, Linux/Unix datetime variables store the number of milliseconds, not the number of days.

[Vegan]

I guess I need to use a more conservative approach

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<script type="text/javascript">

//Set the two dates
var millennium =new Date(2000, 0, 1) //Month is 0-11 in JavaScript
today=new Date()
//Get 1 day in milliseconds
var one_day=1000*60*60*24

//Calculate difference btw the two dates, and convert to days
document.write(Math.ceil((today.getTime()-millennium.getTime())/(one_day))+
" days has gone by since the millennium!")

</script>
 

[Vegan]

do I need to check to see if that function will work all the time, such as detect the OS in use?

[califdon]

I guess I need to use a more conservative approach

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<script type="text/javascript">

//Set the two dates
var millennium =new Date(2000, 0, 1) //Month is 0-11 in JavaScript
today=new Date()
//Get 1 day in milliseconds
var one_day=1000*60*60*24

//Calculate difference btw the two dates, and convert to days
document.write(Math.ceil((today.getTime()-millennium.getTime())/(one_day))+
" days has gone by since the millennium!")
</script>

Are you sure you want to use Math.ceil? That rounds upward.

I did it this way, which seems to work:

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<script type='text/javascript'>
   var millennium = new Date(2000, 0, 1);
   var today = new Date();
   var difference_ms = today - millennium;
   var ms_in_a_day = 1000 * 60 * 60 * 24;
   var difference_days = Math.round(difference_ms / ms_in_a_day);
   document.write("Today is "+ difference_days + " days after the millennium.");
</script>

You might want to wrap it in a function, as in this example:
http://www.mcfedries.com/javascript/daysbetween.asp

do I need to check to see if that function will work all the time, such as detect the OS in use?

No, Javascript should work the same, regardless of what OS the browser is running in. If your algorithm is correct, it will work.