How to load javascript files with a progress bar

Here is a crossbrowser code for a preloader:

var preloaderID = 'preloader';
var contentID = 'mainContent';
var TagList = new Array('div','img');

var IMGqueue = new Array();
var queueItem = 0;
var preloading = false;

function checkURL(URLstring){
    if((URLstring != 'none') && (URLstring.length > 0)){
        return URLstring.substring(URLstring.indexOf("(") + 1, URLstring.indexOf(")"));
    }else{
        return false;
    }
}

function checkBrowser(StyleSheet){
    if (document.styleSheets[StyleSheet].cssRules)
        return document.styleSheets[StyleSheet].cssRules;
    else
        return document.styleSheets[StyleSheet].rules;
}

function enqueueBgImg(imgPath){
    var isInArray = false;
    for(queueItem = 0; queueItem < IMGqueue.length; queueItem++){
        if(imgPath == IMGqueue[queueItem]){
            isInArray = true;
        }
    }
    if(!isInArray){IMGqueue.push(imgPath)};
}

function parseStyleSheets(tagName, tagClass){
    var styleSheet;
    for(styleSheet = 0; styleSheet < document.styleSheets.length; styleSheet++){
        var AllRules = checkBrowser(styleSheet);
        var Rule;
        for(Rule = 0; Rule < AllRules.length; Rule++){
            var ruleName = AllRules[Rule].selectorText.toUpperCase();
            if((ruleName.indexOf(tagName.toUpperCase()) > -1 ) || (ruleName.indexOf(tagClass.toUpperCase()) > -1)){
                var RuleBG = AllRules[Rule].style.backgroundImage;
                if(checkURL(RuleBG)){enqueueBgImg(checkURL(RuleBG))};
            }
        }
    }
}

function checkIMG(IMGtoLoad){
    if(IMGtoLoad.complete){
        clearInterval(IMGinterval);
        preloading = false;
    }
}

function preload(){
    if((!preloading) && (queueItem < IMGqueue.length)){
        preloading = true;
        document.IMG = new Image;
        document.IMG.src = IMGqueue[queueItem];
        IMGinterval = setInterval("checkIMG(document.IMG)",50);
        queueItem++;
    }
    if(queueItem >= IMGqueue.length){
        clearInterval(mainInterval);
        document.getElementById(preloaderID).style.display = 'none';
        document.getElementById(contentID).style.display = '';
    }
}

function preloadBgImgs(){
    var TagName,TAG;
    for(TagName = 0; TagName < TagList.length; TagName++){
        var TagArray = document.getElementsByTagName(TagList[TagName]);
        for(TAG = 0; TAG < TagArray.length; TAG++){
            var styleBG = TagArray[TAG].style.backgroundImage;
            if(checkURL(styleBG)){enqueueBgImg(checkURL(styleBG))};
            parseStyleSheets(TagList[TagName], TagArray[TAG].className );
        }
    }
    queueItem = 0;
    mainInterval = setInterval("preload()",50);
}



preloaderID: ID of the element that will be visible till the page is totally loaded (a div, something, with a message for the user)
contentID: ID of the element with the desired content, element that must have the setting display:none
TagList: TAGs that will be verified by the script in order to establish if they have a background picture, so that the picture is loaded before the webpage.
In body you must put: onload='preloadBgImgs();'

Regards,
Wesley