只需将其分成3零件..第一周，上周和之间，这样的东西：

Just divide it into 3 parts.. first week, last week and the in between, something like this:

function workday_count(start,end) {
  var first = start.clone().endOf('week'); // end of first week
  var last = end.clone().startOf('week'); // start of last week
  var days = last.diff(first,'days') * 5 / 7; // this will always multiply of 7
  var wfirst = first.day() - start.day(); // check first week
  if(start.day() == 0) --wfirst; // -1 if start with sunday 
  var wlast = end.day() - last.day(); // check last week
  if(end.day() == 6) --wlast; // -1 if end with saturday
  return wfirst + days + wlast; // get the total
}

测试代码

var ftest = {date:'2015-02-0',start:1,end:7};
var ltest = {date:'2015-02-2',start:2,end:8};
var f = 'YYYY-MM-DD';
for(var z=ftest.start; z<=ftest.end; ++z) {
  var start = moment(ftest.date + z);
  for(var y=ltest.start; y<=ltest.end; ++y) {
    var end = moment(ltest.date + y);
    var wd = workday_count(start,end);
    console.log('from: '+start.format(f),'to: '+end.format(f),'is '+wd+' workday(s)');
  }
}

输出测试代码：

from: 2015-02-01 to: 2015-02-22 is 15 workday(s)
from: 2015-02-01 to: 2015-02-23 is 16 workday(s)
from: 2015-02-01 to: 2015-02-24 is 17 workday(s)
from: 2015-02-01 to: 2015-02-25 is 18 workday(s)
from: 2015-02-01 to: 2015-02-26 is 19 workday(s)
from: 2015-02-01 to: 2015-02-27 is 20 workday(s)
from: 2015-02-01 to: 2015-02-28 is 20 workday(s)
from: 2015-02-02 to: 2015-02-22 is 15 workday(s)
from: 2015-02-02 to: 2015-02-23 is 16 workday(s)
from: 2015-02-02 to: 2015-02-24 is 17 workday(s)
from: 2015-02-02 to: 2015-02-25 is 18 workday(s)
from: 2015-02-02 to: 2015-02-26 is 19 workday(s)
from: 2015-02-02 to: 2015-02-27 is 20 workday(s)
from: 2015-02-02 to: 2015-02-28 is 20 workday(s)
from: 2015-02-03 to: 2015-02-22 is 14 workday(s)
from: 2015-02-03 to: 2015-02-23 is 15 workday(s)
from: 2015-02-03 to: 2015-02-24 is 16 workday(s)
from: 2015-02-03 to: 2015-02-25 is 17 workday(s)
from: 2015-02-03 to: 2015-02-26 is 18 workday(s)
from: 2015-02-03 to: 2015-02-27 is 19 workday(s)
from: 2015-02-03 to: 2015-02-28 is 19 workday(s)
from: 2015-02-04 to: 2015-02-22 is 13 workday(s)
from: 2015-02-04 to: 2015-02-23 is 14 workday(s)
from: 2015-02-04 to: 2015-02-24 is 15 workday(s)
from: 2015-02-04 to: 2015-02-25 is 16 workday(s)
from: 2015-02-04 to: 2015-02-26 is 17 workday(s)
from: 2015-02-04 to: 2015-02-27 is 18 workday(s)
from: 2015-02-04 to: 2015-02-28 is 18 workday(s)
from: 2015-02-05 to: 2015-02-22 is 12 workday(s)
from: 2015-02-05 to: 2015-02-23 is 13 workday(s)
from: 2015-02-05 to: 2015-02-24 is 14 workday(s)
from: 2015-02-05 to: 2015-02-25 is 15 workday(s)
from: 2015-02-05 to: 2015-02-26 is 16 workday(s)
from: 2015-02-05 to: 2015-02-27 is 17 workday(s)
from: 2015-02-05 to: 2015-02-28 is 17 workday(s)
from: 2015-02-06 to: 2015-02-22 is 11 workday(s)
from: 2015-02-06 to: 2015-02-23 is 12 workday(s)
from: 2015-02-06 to: 2015-02-24 is 13 workday(s)
from: 2015-02-06 to: 2015-02-25 is 14 workday(s)
from: 2015-02-06 to: 2015-02-26 is 15 workday(s)
from: 2015-02-06 to: 2015-02-27 is 16 workday(s)
from: 2015-02-06 to: 2015-02-28 is 16 workday(s)
from: 2015-02-07 to: 2015-02-22 is 10 workday(s)
from: 2015-02-07 to: 2015-02-23 is 11 workday(s)
from: 2015-02-07 to: 2015-02-24 is 12 workday(s)
from: 2015-02-07 to: 2015-02-25 is 13 workday(s)
from: 2015-02-07 to: 2015-02-26 is 14 workday(s)
from: 2015-02-07 to: 2015-02-27 is 15 workday(s)
from: 2015-02-07 to: 2015-02-28 is 15 workday(s)