manipulating date object with javascript

Question

i have been tinkering with the date object.

I want to add a dynamic amount of days to a day and then get the resulting date as a variable and post it to a form.

var startDate = $('#StartDate').datepicker("getDate");
    var change = $('#numnights').val();
    alert(change);
    var endDate = new Date(startDate.getFullYear(), startDate.getMonth(),startDate.getDate() + change);

does everything correctly except the last part. it doesnt add the days onto the day

take this scenario:
startdate = 2011-03-01   
change = 1  
alert change = 1
endDate = 2011-03-11 *it should be 2011-03-02*

thank you to all the quick replies.

converting change variable to an integer did the trick. thank you.

parseInt(change)

just to extend on this: is there a way to assign a variable a type, such as var charge(int)?

nybbler · Accepted Answer · 2011-01-25 03:42:23Z

2

You may have fallen victim to string concatenation.

Try changing your last parameter in the Date constructor to: startDate.getDate() + parseInt(change)

See this example for future reference.

answered Jan 25, 2011 at 3:42

nybbler

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4 Comments

JS1986 Over a year ago

changing the variable to an integer worked. however, if the day goes into a new month the month stays the same.

nybbler Over a year ago

It shouldn't. For example, if you called var dt = new Date(2010, 11, 32); your dt object will contain January 1, 2011. The Date constructor handles overflow of months and days. I can set up an example for you to see if you like.

nybbler Over a year ago

Hopefully this example helps clear things up for you: webdevout.net/test?01d

JS1986 Over a year ago

// NOTE: Months are indexed from 0. So 0 = January and 11 = December this examples a lot! :)

Metal · Accepted Answer · 2011-01-25 03:43:45Z

1

convert change to a number before adding it. it looks like you're getting a string concatenation operation rather than the addition you're expectingin your code.

answered Jan 25, 2011 at 3:43

Metal

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Comments

Lance · Accepted Answer · 2011-01-25 03:44:05Z

1

I believe you are concatenating instead of using the mathematical operator. Try this instead,

var endDate = new Date(startDate.getFullYear(), startDate.getMonth(),startDate.getDate() + (+change));

answered Jan 25, 2011 at 3:44

Lance

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Comments

jondavidjohn · Accepted Answer · 2011-01-25 03:47:51Z

1

It looks like you are not adding the ending day, you are concatinating it so '1' + '1' = '11'

use parseInt() to make sure you are working with integers

example

var change = parseInt($('selector').val());

Also, with this solution, you could easily end up with a day out of range if you are say on a start date of the 29th of the month and get a change of 5

answered Jan 25, 2011 at 3:47

jondavidjohn

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