Question

I have a date object and I need to create another date object that is 1 week after the first date object. I already have an implementation but it seems that there is a bug with javascript when it reaches the months of October, November and December. Is there a workaround for this? Note that the behavior is consistent across Chrome, FF and IE.

        // ************ TEST#1 ************
        var startDate = new Date(2011,08,05); // set to Sept 5, 2011
        alert('START DATE' + startDate);

        var endDate = new Date();
        endDate.setDate(startDate.getDate() + 7);

        alert('END DATE' + endDate); // endDate is Sept 12 which is correct
        // check that startDate's value is unchanged
        alert('START DATE' + startDate); 


        // ************ TEST#2 ************
        var startDate = new Date(2011,10,05); // set to Nov 5, 2011
        alert('START DATE' + startDate);

        var endDate = new Date();
        endDate.setDate(startDate.getDate() + 7);

        alert('END DATE' + endDate); // endDate is Sept 12, 2011 which is wrong
        alert('START DATE' + startDate);



        // ************ TEST#3 ************
        // changed implementation but this won't work
        var startDate = new Date(2011,10,05);
        alert('START DATE' + startDate);

        var endDate = startDate;
        endDate.setDate(startDate.getDate() + 7);

        alert('END DATE' + endDate); // endDate is correct but...
        alert('START DATE' + startDate); // startDate's value has changed as well

Answer 1

I think your error might be that you are setting endate to today.

    // ************ TEST#2 ************
    var startDate = new Date(2011,10,05); // set to Nov 5, 2011
    alert('START DATE' + startDate);

    // edit
    var endDate = new Date(startDate.getFullYear(),startDate.getMonth(),startDate.getDate() + 7);
    // old var endDate = new Date();
    // endDate.setDate(startDate.getDate() + 7);

    alert('END DATE' + endDate); // endDate is Sept 12, 2011 which is wrong
    alert('START DATE' + startDate);