I think a lot of people looking how to use javascript built the date picker with start date and end date. Normally how we did is just create 2 field with START DATE and END DATE. but the END DATE still can choose early then START DATE.
And we only can using javascript code to solve it.
How to do that? You can using javascript plugin call PopCalXP9_Lite. and it already have the function call DateRange.
End Date cannot early then Start Date.
Start Date cannot late then End Date.
For jQuery Date Picker