Snippet to how to preload images assets using javascript.

javascript-image-preloader

function preloadimages(arr) {
    var newimages = []
        , loadedimages = 0
        , postaction = function() {}
        , arr = ( typeof arr != "object" ) ? [arr] : arr
        , i = 0;

    function imageloadpost(){
        loadedimages++;
        if ( loadedimages == arr.length ) {
            postaction( newimages ) //call postaction and pass in newimages array as parameter
        }
    }

    for ( ; i < arr.length; i++ ){
        newimages[i] = new Image();
        newimages[i].src = arr[i];
        newimages[i].onload = function() {
            imageloadpost();
        }
        newimages[i].onerror = function() {
            imageloadpost();
        }
    }

    return { //return blank object with done() method
        done: function(f){
            postaction = f || postaction //remember user defined callback functions to be called when images load
        }
    }

}

// How to use it?!
var arr = [
    '_res/images/Gallery/img01.png',
    '_res/images/Gallery/img02.png',
    '_res/images/Gallery/img03.png'
];

preloadimages(preLoadedImgs).done(function(images){
    for ( var i = 0; i < images.length; i++ ) {
        console.log('image src' + images[i].src + 'preloaded!' );
    }
});