jQuery test for if a div is the first child?

How to do test if a image is the first or the last of a group of images?

I'm trying to make previous and next buttons animate in or 开发者_开发百科out depending on whether I'm at the end of a series of images with the following code:

var $current = jQuery("img .active");
var $next = $current.next();

if ($next != jQuery("img:first-child")
{
 // show next item and the previous button
 // seems to work?

} else if ($next == jQuery("img:last-child")
{
 // hide the next button since we're at the end
 // doesn't seem to work??
}

---

You want to check the index of the img:

var $current = jQuery("#img .active"),
    index = $current.index();

if (index === 0) {
    // This is the first
} else if (index === jQuery("#img").children().length - 1) {
    // This is the last
}

---

Assuming no big performance hit from using .each() I would do something like this:

jQuery('#img').children().each(function(i,obj){
  // some code to show buttons
  if (i <= 0) { // hide prev }
  if (i >= $('#img').children().length - 1) { // hide next }
});

Then hide all $('#img').children() except for the active one, or however you want it to function.