How to prevent this strange jQuery .animate() lag?

Question

See demo: jsFiddle

• I have a simple form that is being toggled when clicking 'show' / 'cancel'
• Everything works fine, but if you click 'cancel' shortly after the form is revealed, there's a good 2-3 seconds lag before the animation even begins.
• This doesn't happen if you wait a few seconds before clicking 'cancel'.
• The lag occures in all tested browsers (ie, ff, chrome).

1. What could cause this lag and how can it be prevented?

2. Is there a better way of coding this sequence of animations, that might prevent any lags?

HTML:

<div id="newResFormWrap">
    <form id="newResForm" action="" method="post" name="newRes">
        <div id="newResFormCont">
            <h3>title</h3>
            <p>form!</p>
            <div class="button" id="cancelNewRes">Cancel</div>
        </div>
    </form> 
</div>
<div class="button" id="addRes">show</div>

jQuery:

$("#newResForm").css({opacity: 0});

$("#addRes").click(function () {
    toggleNewRes()
});
$("#cancelNewRes").click(function () {
    toggleNewRes()
});

//toggleNewRes
function toggleNewRes() {
    if ($("#newResFormWrap").css('display') == "none") {//if hidden 
        $("#addRes").animate({ opacity: 0 }, 'fast', function() {
            $("#newResFormWrap").toggle('fast', function (){
                $("#newResForm").animate({ opacity: 100 },2000);
            });
        });
    } else { //if visible
        $("#newResForm").animate({ opacity: 0 }, 100,function() {
            $("#newResFormWrap").toggle('fast', function (){
                $("#addRes").animate({ opacity: 100 });
            });
        });
    }
}

Answer 1

Make sure to clear the queue when starting a new animation with stop():

$("#newResForm").stop().animate({ opacity: 0 }, 100,function() {
        $("#newResFormWrap").toggle('fast', function (){
            $("#addRes").animate({ opacity: 100 }); 
                 // ...

What's causing the lag is the fact that your long 2-second animation $("#newResForm").animate({ opacity: 100 },2000) isn't finished yet. JQuery puts animations by default into a queue, waiting for one to finish before the next begins. You clear the queue with stop(), which is especially useful if you have two contradicting animations (like an open and close animation, or a mouseover/mouseout animation). In fact you might find it a good practice to begin all your animation chains with stop() unless you know you want them to queue with prior animations that may have occurred elsewhere.

Getting into more advanced topics, you can even name different queues, so that for example your hover animations and your expand/collapse animations are treated separately for the purposes of stop(). See the queue option (when given a string) at http://api.jquery.com/animate/ for more details.

Answer 2

Try to use stop() :

Here is jsfiddle.

if ($("#newResFormWrap").is(':visible')) {//this way is eaiser to check
    $("#addRes").stop(true,false).animate({ opacity: 0 }, 'fast', function() {
        $("#newResFormWrap").toggle('fast', function (){
            $("#newResForm").animate({ opacity: 100 },2000);
        });
    });
}