gistfile1.js

function inMinutes(time) {
  return time.getHours() * 60 + time.getMinutes();
}

function calcDuration(timeStart, timeEnd) {
  if (!timeStart || !timeEnd) {
    return "";
  }
  
  var start = inMinutes(timeStart);
  var end = inMinutes(timeEnd);
  var result = "";
  
  if (end < start) {
    end += 24 * 60;
  }
  
  var offset = end - start;
  
  if (offset >= 60) {
    var hour = Math.floor(offset / 60);
    var minute = offset % 60;
    
    if (minute > 0) {
      result = hour + "小时" + minute + "分钟";
    } else {
      result = hour + "小时";
    }    
  } else {
    result = offset + "分钟";
  }
  
  return result;
}