Question

I’m adding days to a specific date:

myDate.setDate(myDate.getDate()+plusdays

Where plusdays is my variable, everything works fine.

Now I would like to calculate the result in a way that permits to skip a given period of time (eventually specified by the user) (e.g. from 1 of April until 15 of April), which is not necessarly an holiday.

I have reviewed the similar questions but either I don’t understand them, or I guess they don’t really solve my problem.

Any ideas?

EDIT: my main problem is that the days should be skipped only when relevant to the calculation. In other words, I need a solution that if I ad 30 days to 28 march, it adds 30 days without counting between 1 aprile – 15 april, but if I add 1 day to 28 march, then the result is simply 29 march.

Answer 1

In the logic of your current code it should be something like

myDate.setDate(myDate.getDate() + plusdays + skipdays)

To calculate skipdays use

var singleDay = 1000 * 60 * 60 * 24,
    fromdate = new Date('1 Apr 2012'),
    todate = new Date('15 Apr 2012'),
    skipdays = (todate - fromdate) / singleDay ;

---

update

After your comment you can use

function interSectionInDays(include, exclude){
    if (!(include.from > exclude.to) && !(include.to < exclude.from)){
        var from = Math.max(include.from, exclude.from),
            to   = Math.min(include.to, exclude.to),
            singleDay = 1000 * 60 * 60 * 24;

        return (to-from)/singleDay;
    }
    return 0;
}

This method will calculate the number of intersected days between to date ranges..

Use as

interSectionInDays( {from: <startdate>, to:<enddate>}, {from:<excludestartdate>, to:<excludeenddate>} );

So in your example

var fromdate = new Date(myDate),
    todate = new Date(fromdate).setDate( fromdate.getDate() + plusdays),
    excludestart = new Date('1 Jan 2012'),
    excludeend = new Date('5 Apr 2012'),
    skipdays = interSectionInDays( {from:fromdate, to:todate}, {from:excludestart, to:excludeend});

myDate.setDate( myDate.getDate() + plusdays + skipdays );

Demo at http://jsfiddle.net/gaby/mACmW/