Continuous animation on hover (performance)

Question

I've created a jQuery function that scrolls a DIV by decreasing the left-margin of the element. It works, but it's incredibly slow. It eats up 100% CPU in no time :s

$(".scroll").hover(
    function () {
        var scroll_offset = parseInt($('#content').css('margin-left'));
        sliderInt = self.setInterval(function(){
            $content.css({'margin-left':scroll_offset+'px'});
            scroll_offset--;
        },8);
    }, 
    function () {
        clearInterval(sliderInt);
    }
);

Obviously I am running this function every 8ms, which is asking a lot. I'm already cacheing my selectors, so I don't know what I can do to improve performance. Am I just going about it the wrong way?

Answer 1

function play () {
  $('#ball').animate({left: '+=20'}, 100, 'linear', play);
}

function pause () {
  $('#ball').stop();
}

$("#bar").hover( play, pause );

#bar {
  margin-top: 20px;
  background: #444;
  height: 20px;
}
#bar:hover #ball {
  background: lightgreen;
}

#ball {
  position: relative;
  left: 0;
  width: 20px;
  height: 20px;
  background: red;
  border-radius: 50%;
}

<div id="bar">
  <div id="ball"></div>
</div>

<script src="//code.jquery.com/jquery-3.1.0.js"></script>

This is really simple without the setInterval or even setTimeout.

• The only important thing is to know that .animate() accepts a function callback, ideal for our purpose to create loop a function. Make sure to use the linear easing instead of the default 'swing' to make our loop constant.
• To stop our animations we can use stop() to prevent animation buildups.
• Simply create 2 functions and use them in your hover method.

---

Using CSS3

and toggling play/pause classes using jQuery:

function play() {
  $('#ball').addClass("play").removeClass("pause");
}

function pause() {
  $('#ball').addClass("pause"); // don't remove .play here
}

$("#bar").hover(play, pause);

#bar {
  margin-top: 20px;
  background: #444;
  height: 20px;
}
#bar:hover #ball {
  background: lightgreen;
}
#ball {
  position: relative;
  left: 0;
  width: 20px;
  height: 20px;
  background: red;
  border-radius: 50%;
}

.play {
  animation: ball-anim 5s infinite linear;
}
.pause {
  animation-play-state: paused;
}
@keyframes ball-anim {
  0%   { left: 0; }
  50%  { left: calc(100% - 20px); }
  100% { left: 0; }
}

<div id="bar">
  <div id="ball"></div>
</div>

<script src="//code.jquery.com/jquery-3.1.0.js"></script>