Filter out non-contiguous date using momentjs and

I want to find the last date that is contiguous with all the previous dates in a list.

Pictorially:

In the above picture I want the circled 'date'.

I have a service that exposes a function (copied from memory, as I am not currently at work):

var maxContiguousDates = function(listOfDates1, listOfDates2){
    ranges = combineDatesIntoTwixRanges(listOfDates1, listOfDates2);
    //Sort with earliest start first
    sortedRanges = _.sortBy(ranges,function(range){return -range.start.unix()})
    return moment.max(sortedRanges.filter(function(range,index){
        var currentRange = range;
        var previousRange = undefined;
        if(index){
            previousRange = sortedRanges[index-1];
        }
        return previousRange?previousRange.overlap(currentRange):true;
    }).end) //I don't remember the specifics I think there is a mistake in this version of the code - the copy at work runs and works for contiguous dates
}

The ternary if statement at the end is supposed to ensure that if no dates are contiguous, then the first should be taken.

However in my test, where I enter a list of non-contiguous dates, it returns the last total date.

I feel like, except if I have made a minor small mistake, this method should work.

Is there a better approach? I didn't see a clever sort, or contiguousness function in momentjs or twix.js. Nor do I see any other way of doing this.

Please let me know if you can see why this would not work as intended, or if there is a better approach.

N.B. this does not pass tests, so it's not appropriate for codereview.stackexchange.com

The problem is that you have not defined a way or getting dates out of the filter. Also, your filter won't stop when you get a non-contiguous date range.

Below is the modification I made

var maxContiguousDate = function(listOfDates1, listOfDates2){
    ranges = combineDatesIntoTwixRanges(listOfDates1, listOfDates2);
    //Sort with earliest start first
    sortedRanges = _.sortBy(ranges,function(range){return -range.start.unix()})
    //combine all ranges if they overlap, or the previous range as a short circuit
    contiguousRange = sortedRanges.reduce(function(previousRange,currentRange){
        if(previousRange.overlaps(currentRange)){
            return previousRange.union(currentRange);
        }else{
             return previousRange;
        })
        return contiguousRange.end;
}