Question

Sorry I could not find this.

$('div#loader').slideDown("fast").delay(1.5);

Does not word as expected, I want it to slideDown, then stay in that mode for 1.5 seconds and then the load function which happens very fast and then it slides up using fast. I thought delay(); was the correct approach.

Full function for those who wish to see:

$(document).ready(function () {
    function last_msg_funtion() {
        var ID = $(".pic_box:last").attr("id");
        $('div#loader').slideDown("fast").delay(1.5);
        $.post("/?action=get&id=" + ID,
        function (data) {
            if (data!="") {
                $(".pic_box:last").after(data);
            }
            $('div#loader').slideUp("fast");
        });
    };
});

Answer 1

You could define a wait helper function and run your code after waiting for 1.5 secs:

$.wait = function(time) {
  return $.Deferred(function(dfd) {
    setTimeout(dfd.resolve, time);
  });
}


$(document).ready(function () {
    function last_msg_funtion() {
        var ID = $(".pic_box:last").attr("id");
        $('div#loader').slideDown("fast");
        $.wait(1500).then(function() {
            $.post("/?action=get&id=" + ID, function (data) {
                if (data != "") {
                    $(".pic_box:last").after(data);
                }
                $('div#loader').slideUp("fast");
            });
        });
    };
});

The wait function makes your code reads better IMO