Answers for "javascript get duration in hours between two timestamps"

javascript get hours difference between two dates

// date1 and date2 are date objects

let hours = Math.abs(date1 - date2) / 36e5;

// The subtraction returns the difference between the two dates in milliseconds.
// 36e5 is the scientific notation for 60*60*1000, dividing by which converts
// the milliseconds difference into hours.

javascript time between two times

You can just subtract the hours right away doing it this way

var valuestart = $("select[name='timestart']").val();
var valuestop = $("select[name='timestop']").val();

//create date format          
var timeStart = new Date("01/01/2007 " + valuestart).getHours();
var timeEnd = new Date("01/01/2007 " + valuestop).getHours();

var hourDiff = timeEnd - timeStart;             
Here's the working fiddle http://jsfiddle.net/VnwF7/4/

UPDATE - to calculate if we are including the next day. Just add the following if block

 if (hourDiff < 0) {
    hourDiff = 24 + hourDiff;
 }
http://jsfiddle.net/gfvhqat9/