jQuery: Animate Margins to Auto?

Question

I'm trying to animate an image so that it centers itself. Here's the code I'd like to use:

$('#myImage').animate({'margin-right': 'auto'});

But when I do that, it's ignored and doesn't change the margin.
Is there a way to animate a margin to auto, or otherwise center an image?

Thanks!

Answer 1

As 'auto' isn't a number, jQuery cannot animate it.

If you are okay with taking the image out of the flow of the document, you can set position to absolute or fixed and try:

$('#myImage').animate({'left': '50%', 'margin-left': -$('#myImage').width()/2 });

Answer 2

You cannot animate an auto property. To properly animate the element to the center of the screen you will need to position it absolutely (or other) and then calculate the screen size, element size, and scroll position. Here is a another SO answer on something similar. Here is the Fiddle

jQuery.fn.center = function () {
    this.css("position","absolute");
    var top = ( $(window).height() - this.height() ) / 2+$(window).scrollTop() + "px",
        left = ( $(window).width() - this.width() ) / 2+$(window).scrollLeft() + "px";
    this.animate({top: top, left: left});
    return this;
}

Alternatively if you only want the horizontal alignment you can remove the top from the animate function. And if you really want to get creative you can remove the position:absolute, and reposition margin:auto after the animation in case of screen resizing. See another fiddle.

jQuery.fn.center = function () {
    this.css("position","absolute");
    var left = ( $(window).width() - this.width() ) / 2+$(window).scrollLeft() + "px";
    this.animate({left: left}, function(){
        $(this).css({position: 'static', margin: '0 auto'});
    });
    return this;
}
$('#selector').center();

Answer 3

Expanding on Josiah Ruddell's answer. If you guys need your image to keep its flow in the document, use this modified version of Josiah's answer. My image was originally positioned at margin: 0 -1000px, and slides in to the calculated margin left and right. While keeping its flow in the dom the whole time

jQuery.fn.center = function () {
  var margin = ( $(window).width() - this.width() ) / 2;
  this.animate({
    marginLeft: margin, 
    marginRight: margin
  }, function(){
    $(this).css({margin: '0 auto'});
  });
  return this;
}