なんか

gistfile1.js

(function(){
  
  var token=(parseInt(Math.random()*10000000000)+'').substr(0,9);
  if(document.getElementById(token) == undefined){
    var r = document.createElement('div');
    var b = document.createElement('button');
    r.id=token;
    b.clicked=false;
    b.innerHTML='GET';
    b.onclick=function(){
      var url = b.clicked ? '/sets/'+token+'/next.json?mix_id='+mix.id : '/sets/'+token+'/play.json?mix_id='+mix.id ;
      aj(url, callback);
    };
    var head = document.getElementById('head');
    head.appendChild(b);
    head.appendChild(r);
  }
  
  function cl(o){
    var a = document.createElement('a');
    a.href=o.item;
    a.appendChild(document.createTextNode(o.contributor+' -- '+o.title));
    var div = document.createElement('div');
    div.appendChild(a);
    return div;
  }

  function callback(res, status){
    if (res == '' || status != 200) {
      return; // ooohhhh
    }
    var j,o;
    eval("j="+res);
    if(j.track.trackId==0){
      b.disabled=true;
      b.style.display='none';
      return;
    }
    o=j.track;
    document.getElementById(token).appendChild(cl(o));
    b.clicked=true;
  }

  function aj(url, func){
    var xhr =(window.XMLHttpRequest)?new XMLHttpRequest():new ActiveXObject("Microsoft.XMLHTTP");
    xhr.onreadystatechange=function(){if(xhr.readyState==4){func(xhr.responseText, xhr.status);}}
    xhr.open("GET", url);
    xhr.send(null);
  }
})()