Jquery 如何将预加载添加到此脚本？

如何将预加载的gif添加到此脚本，使其显示，直到加载幻灯片中的所有图像

function slideSwitch() {

var $active = $('#slideshow IMG.active');

if ( $active.length == 0 ) $active = $('#slideshow IMG:last');

// use this to pull the images in the order they appear in the markup
var $next =  $active.next().length ? $active.next()
    : $('#slideshow IMG:first');

// uncomment the 3 lines below to pull the images in random order

// var $sibs  = $active.siblings();
// var rndNum = Math.floor(Math.random() * $sibs.length );
// var $next  = $( $sibs[ rndNum ] );


$active.addClass('last-active');

$next.css({opacity: 0.0})
    .addClass('active')
    .animate({opacity: 1.0}, 1500, function() {
        $active.removeClass('active last-active');
    });    }

$(function() {
setInterval( "slideSwitch()", 5000 );
});

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预加载图像可以是CSS背景图像。加载图像时，背景将不可见