Preload an image before calling a callback function

preloadImage.js

var preloadImage = function(url, callback) {
    var loaded = false,
    loadHandler = function() {
        if (!loaded) {
            callback(url);
        }
        loaded = true;
    },
    img = $('<img>')
        .one('load', loadHandler)
        .attr('src', url);
    if ($(img).first().complete) {
        loadHandler(url);
    }
}

preloadImageWithoutJQuery.js

var preloadImage = function(url, callback) {
    var loaded = false,
        loadHandler = function() {
            if (!loaded) {
                callback(url);
            }
            loaded = true;
        },
        img = document.createElement('img');
    img.addEventListener('load', loadHandler);
    img.src = url;
    if (img.complete) {
        loadHandler();
    }
}