Call a Javascript function after the slider control is left from mouse?

Question

I am using the slider control from WebFX. I want to invoke a function called process() after the slider is dragged in mouse and left. I used the following code:

var s1 = new Slider(document.getElementById("slider-1"), document.getElementById("slider-input-1"),"vertical");
s1.onchange= function()
{
process();
}

But the problem here is the function is called on a single value change in the slider. That is , when we click and drag the slider it calls the function for every change in value.
But what I want is to invoke the function only when the slider is left after dragging. Not invoke the function for each change while dragging the slider control.

How to accomplish this?

Answer 1

Helped myself with onmouseup mouse event on the div that contains the slider. And that helped but with a small flaw.
When the user drags the mouse holding the slider and releases the mouse after moving out of the div containing the slider the event is not generated.

Any other solution overcoming this flaw would be good.