I've tried to unbind this :
 var foo = $(".js_slide").bind('click' , function () {
  var $contentBlock = $(this).next("li[id^=content_]");
if ($contentBlock.hasClass("is_open")) {
    $contentBlock.animate({
        width: '0%'
    }).removeClass("is_open");
        } 
else {
    // if a content box is open (=> an element with the class .is_open exists), close it
    $(".js_content.is_open").animate({
        width: '0%'
    }).removeClass("is_open");
    $contentBlock.animate({
        width: '45%'        
    }, 500).addClass("is_open");      
}                               
});
With the following piece of code ,but someting goes wrong and i can't figure it out what it could be
$('.js_slide').unbind('click', foo);
 
     
    