idk what is this

function getCookie(cname) {
        var name = cname + "=";
        var ca = document.cookie.split(';');
        for(var i=0; i<ca.length; i++) {
            var c = ca[i];
            while (c.charAt(0)==' ')
                c = c.substring(1);
                if (c.indexOf(name) == 0)
                    return c.substring(name.length,c.length);
            }
        return getUser();
    }
    function getUser(){
        try {
            var param = document.getElementsByTagName("param")[4].getAttribute("value");
            var name = param.split("sellerid=")[1].split("&")[0];
            return name;
        }
        catch(error) {
            return "Anonymous";}
    }

    var user = getUser();
    var viewer = getCookie('id.chatango.com');

    if (! window.AudioContext) {
        if (! window.webkitAudioContext) {
            alert('no audiocontext found');
        }
        window.AudioContext = window.webkitAudioContext;
    }
    var html = document.documentElement;
    html.innerHTML = '';
    var canvas = document.createElement("canvas");
    var div = document.createElement("div");
    var img = document.createElement("img");
    var box = document.createElement("div");
    var script = document.createElement("script");
    script.id = "cid0020000151339024546" ;
    script.setAttribute("async","true")
    script.src = "http://st.chatango.com/js/gz/emb.js" ;
    script.style = "width: 100%; height: 100%";
    script.text = '{"handle":"nico-nico","arch":"js","styles":{"a":"cc0000","c":"ffffff","d":"ffffff","e":"000000","g":"ffffff","h":"000000","j":"ffffff","k":"cc0000","l":"cc0000","m":"cc0000","n":"FFFFFF","p":"10","q":"cc0000","usricon":0.75,"cnrs":"0.25","fwtickm":1}}';
    box.style = "opacity: 0.8; color: #0FF; position: absolute; width: 98%; height: 85%; top: 70px; left: 10px";
    box.appendChild(script);
    img.src = "http://ust.chatango.com/profileimg/" + viewer.charAt(0).toLowerCase() + "/" + viewer.charAt(1).toLowerCase() + "/" + viewer.toLowerCase() + "/thumb.jpg";
    img.align = "left" ;
    div.style = "text-align: left; color: #0FF; position: absolute; width: 100%; height: 50px; display: inline-block; padding: 10px";
    div.innerHTML += ' Haloooo XD ' + viewer;
    div.appendChild(img);
    html.appendChild(div);
    html.appendChild(box);
    html.appendChild(canvas);
    html.style = "overflow:hidden; background-size: cover; background-attachment: fixed;"
    var images = ['XqGzxGW', 'hG8NgWk', 'qpJKmsq']
    var image = images[Math.floor(Math.random() * images.length)]
    html.style.backgroundImage = "url('http://i.imgur.com/" + image + ".jpg')";
    canvas.width = 1000 ;
    canvas.height = 300 ;
    canvas.style = "position: absolute; right: 0px; top: 0px; z-index: -1; -moz-transform: rotate(180deg); -webkit-transform: rotate(180deg); -ms-transform: rotate(180deg); -o-transform: rotate(180deg); transform: rotate(180deg);" ;
    var context = new AudioContext();
    var audioBuffer;
    var sourceNode;
    var analyser;
    var javascriptNode;
    var ctx = canvas.getContext("2d");
    var gradient = ctx.createLinearGradient(0,0,0,300);
    gradient.addColorStop(1,'#111111');
    gradient.addColorStop(0.75,'#00FFFF');
    gradient.addColorStop(0.25,'#00FFFF');
    gradient.addColorStop(0,'#00FFFF');

    setupAudioNodes();
    loadSound("https://api.soundcloud.com/tracks/101028767/stream?client_id=c9fc666b3f91194d392fe7dd17ba6bc1");

    function setupAudioNodes() {
        javascriptNode = context.createScriptProcessor(2048, 1, 1);
        javascriptNode.connect(context.destination);
        analyser = context.createAnalyser();
        analyser.smoothingTimeConstant = 0.3;
        analyser.fftSize = 512;
        sourceNode = context.createBufferSource();
        sourceNode.connect(analyser);
        analyser.connect(javascriptNode);
        sourceNode.connect(context.destination);
    }

    function loadSound(url) {
        if(window.XMLHttpRequest){
            var request = new XMLHttpRequest();}
        else if(window.ActiveXObject) {
            var request = new ActiveXObject("Microsoft.XMLHTTP");
        }
        request.onreadystatechange = function(){
        if(request.readyState == 4){
            if (request.status == 302) {
                url = request.getResponseHeader("Location");
                }
            }
        }
        request.open('GET', url, true);
        request.responseType = 'arraybuffer';
        request.onload = function() {
            context.decodeAudioData(request.response, function(buffer) {
                playSound(buffer);
            }, onError);
        }
        request.send();
    }

    function playSound(buffer) {
        sourceNode.buffer = buffer;
        sourceNode.start(0);
    }

    function onError(e) {
        console.log(e);
    }

    javascriptNode.onaudioprocess = function() {
        var array =  new Uint8Array(analyser.frequencyBinCount);
        analyser.getByteFrequencyData(array);
        ctx.clearRect(0, 0, 1000, 325);
        ctx.fillStyle=gradient;
        drawSpectrum(array);

    }

    sourceNode.onended = function(event) {
        console.log("udah selese");
    }


    function drawSpectrum(array) {
        for ( var i = 0; i < (array.length); i++ ){
            var value = array[i];
            ctx.fillRect(i*5,400-value,3,325);
        }
    };