这应该是窍门

  var start = $（'＃start_date'）。val（）; 
 var end = $（'＃end_date'）。val（）; 

 // end  -  start以毫秒为单位返回差异
 var diff = new Date（end-start）; 

 // get days 
 var days = diff / 1000/60/60/24; 
 

示例

  var start = new Date（2010-04-01），
 end = new Date（），
 diff = new Date（end-start），
 days = diff / 1000/60/60/24; 

天; // => 8.525845775462964 
 

HI Guys,

I have 2 asp.net texboxes with calendar extender. i want to find out the number of days between both dates when one of the date control is changed. how can i achieve this using jquery or javascript ?

This should do the trick

var start = $('#start_date').val();
var end = $('#end_date').val();

// end - start returns difference in milliseconds 
var diff = new Date(end - start);

// get days
var days = diff/1000/60/60/24;

Example

var start = new Date("2010-04-01"),
    end   = new Date(),
    diff  = new Date(end - start),
    days  = diff/1000/60/60/24;

days; //=> 8.525845775462964