Handling of selection through javascript

Please refer to the link of my chart .

http://www.humblesoftware.com/fin开发者_运维问答ance/index (Customized this )

Basically the requirement is that , only one month of selection can be made at a point of time .(From the child chart)

If the selection is made from left side , i am simply adding 30 to the other value

xmin = Math.floor(area.x1);
xmax = xmin+30; 

But if the selection is made from the right side then how to handle this ??

(Means if the xmax is selected first then how can i handle the xmin value )??

Without knowing too much about the situation, something like this should do:

// set the xmin to where they click
xmin = Math.floor(area.x1);

// make x-max the + 30 as you normally do
xmax = xmin + 30;

// now add a check to make sure we're not off the chart
// if we are, make the chart's last possible X value the
// x max, and subtract 30 from that to go backwards (and
// it may be a good idea to check if xmin is under the
// chart's min x value.
if (xmax > chart.xmax){
  xmax = chart.xmax;
  xmin = xmax - 30;
  if (xmin < chart.xmin){
    xmin = chart.xmin;
  }
}