call function within autocomplete jquerry plugin

call function within autocomplete jquerry plugin

I'm work with autocomplete jquerry plugin. but i have face two main
problem on this
Call a function within autocomplete function
Also get the value of textbox to pass with function
Html
<input id="txtDemo" type="text" />
Js
$("#txtDemo").autocomplete({
source: availableTags
});
This is my function, Value is value of textbox
function Demo (value)
{
//code for getting value from code behind in the form of array
}