Hey guys, i found this script a while ago when googling for multiple file uploads, its a nice script but i really find it hard to understand how it works
For instance, i wanna know how do i know when the script has finished, when it finishes uploading i want to redirect to another page for example.

Here is the script:
Code JavaScript:
var sendFile = 4096000;
sendFile = (function(toString, maxSize){
    var isFunction = function(Function){return  toString.call(Function) === "[object Function]";},
        split = "onabort.onerror.onloadstart.onprogress".split("."),
        length = split.length;
    return  function(handler){
        if(maxSize && maxSize < handler.file.fileSize){
            if(isFunction(handler.onerror))
                handler.onerror();
            return;
        };
        var xhr = new XMLHttpRequest,
            upload = xhr.upload;
        for(var
            xhr = new XMLHttpRequest,
            upload = xhr.upload,
            i = 0;
            i < length;
            i++
        )
            upload[split[i]] = (function(event){
                return  function(rpe){
                    if(isFunction(handler[event]))
                        handler[event].call(handler, rpe, xhr);
                };
            })(split[i]);
        upload.onload = function(rpe){
            if(handler.onreadystatechange === false){
                if(isFunction(handler.onload))
                    handler.onload(rpe, xhr);
            } else {
                setTimeout(function(){
                    if(xhr.readyState === 4){
                        if(isFunction(handler.onload))
                            handler.onload(rpe, xhr);
                    } else
                        setTimeout(arguments.callee, 15);
                }, 15);
            }
        };
        xhr.open("post", handler.url || "?upload=true", true);
        xhr.setRequestHeader("If-Modified-Since", "Mon, 26 Jul 1997 05:00:00 GMT");
        xhr.setRequestHeader("Cache-Control", "no-cache");
        xhr.setRequestHeader("X-Requested-With", "XMLHttpRequest");
        xhr.setRequestHeader("X-File-Name", handler.file.fileName);
        xhr.setRequestHeader("X-File-Size", handler.file.fileSize);
        xhr.setRequestHeader("Content-Type", "multipart/form-data");
        xhr.send(handler.file);
        return  handler;
    };
})(Object.prototype.toString, sendFile);
function sendMultipleFiles(handler){
    var length = handler.files.length,
        i = 0,
        onload = handler.onload;
    handler.current = 0;
    handler.total = 0;
    handler.sent = 0;
    while(handler.current < length)
        handler.total += handler.files[handler.current++].fileSize;
    handler.current = 0;
    if(length){
        handler.file = handler.files[handler.current];
        sendFile(handler).onload = function (rpe, xhr) {
            if (++handler.current < length) {
                if (handler.current == length-1) {
                    xhr2 = new XMLHttpRequest;
                    xhr2.open("post", handler.url || "?subm=true", true);
                    xhr2.send();
                }
                handler.sent += handler.files[handler.current - 1].fileSize;
                handler.file = handler.files[handler.current];
                sendFile(handler).onload = arguments.callee;
            } else if (onload) {
                handler.onload = onload;
                handler.onload(rpe, xhr);
            }
        };
    };
    return  handler;
};

Here's how it gets triggered:
Code JavaScript:
onload = function () {
    function size(bytes) {
        var i = 0;
        while (1023 < bytes) {
            bytes /= 1024;
            ++i;
        };
        return i ? bytes.toFixed(2) + ["", " Kb", " Mb", " Gb", " Tb"][i] : bytes + " bytes";
    };
    var input = document.getElementById("pic"),
	sub = document.getElementById("a1").appendChild(document.createElement("span")),
	bar = document.getElementById("a2").appendChild(document.createElement("span")),
	div = document.getElementById("a3"),
    subm = document.getElementById("submit");
    subm.addEventListener("click", function () {
        input.setAttribute("disabled", "true");
        sendMultipleFiles(
	{
		files: input.files,
		onloadstart: function () {
		    div.innerHTML = "מתחיל העלאה";
		    sub.style.width = bar.style.width = "0px";
		},
		onprogress: function (rpe) {
		    div.innerHTML = ["מעלה: " + this.file.fileName,"נשלח: " + size(rpe.loaded) + " מתוך " + size(rpe.total),"סך הכל העלאה: " + size(this.sent + rpe.loaded) + " מתוך " + size(this.total)," אנא המתן עד שתופיע הודעה שהנתונים הועלו בהצלחה."].join("<br />");
		    sub.style.width = ((rpe.loaded * 200 / rpe.total) >> 0) + "px";
		    bar.style.width = (((this.sent + rpe.loaded) * 200 / this.total) >> 0) + "px";
		},
		onload: function (rpe, xhr) {
		    div.innerHTML += ["","✔ העלאת הנתונים הושלמה."].join("<br />");
		    sub.style.width = bar.style.width = "200px";
		    input.removeAttribute("disabled");
		},
		onerror: function () {
			div.innerHTML = "הקובץ: " + this.file.fileName + " גדול מדי, העלאה נכשלה.";
		    input.removeAttribute("disabled");
		}
	});
    }, false);
};

Thanks for the help
ulthane.