JSFiddle - React, Tailwind, and code Playground

HTML

<img class="thumbnail" src="http://www.o3mobi.com/jquery.jpg">
<img class="thumbnail" src="http://www.bioneural.net/wp-content/uploads/2008/02/jquery.jpg">
<img id="fullsized">

CSS

.thumbnail {
    width: 5em;
    height: 5em;
}

#fullsized {
    width: 10em;
    height: 10em;
    border: 2px solid red;
}

JavaScript

$.fn.fadeToSrc = function(src, speedOut, speedIn, callback) {
    return this.fadeOut(speedOut, function() {
        $(this).attr('src', src).fadeIn(speedIn, callback);
    });
};

$(".thumbnail").mouseover(function () {
    var newsrc = $(this).attr("src");
    $("#fullsized").fadeToSrc(newsrc, 1000, 1000);
});