500px following recursive, callback

// 500px page through image gallery (following)
var t1=new Date(),stack=0;tag="following",page=6511;
//tag="following",page=6511;
//tag="rg443/favorites",page=884;
//tag="popular",page=1112;
//tag="editors",page=324;
//tag="upcoming",page=1065;
//tag="fresh/today",page=3361;
//tag="fresh/yesterday",page=1421;
//tag="fresh/week",page=5749;
// tag="blog",page=61;
tag="following",page=100;

/* fetch url */
function get_url(url,callback) {
        var r=new XMLHttpRequest();
        r.open("GET",url,true);
        //r.setRequestHeader("X-Requested-With", "XMLHttpRequest");
        //r.setRequestHeader("Accept-Encoding", "gzip");
        r.onreadystatechange=function(){
       if (this.readyState==4 && this.status==200 && callback) callback.call(this.responseText);
       }
    r.send();

}
/*
Array.prototype.unique = function(){
return this.filter(function(s, i, a){ return i == a.lastIndexOf(s); });
}
*/
function post_imgur(a,callback) {
var r=new XMLHttpRequest();
r.posted=a.length;
r.open("POST","http://176.34.162.148/jabry/imgur1.asp?u=&b=",true);
//r.open("POST","http://notebook1.lan:8000/jabry/imgur1.asp?u=&b=",true);
r.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
r.onreadystatechange=function(){if (this.readyState==4 && this.status==200 && callback) callback.call(this.responseText); }
r.send("u=" + a.join(","));
stack++;
}

function parse_page(s){
   var m=s.toString().match(/http:\/\/pcdn.500px.net\/\d+\/\w+\/\d.jpg/gim);
   m && m.forEach(function(v,i,a){a[i]=v.replace(/\d.jpg$/,"4.jpg")});
   //console.log(m);
   m && post_imgur(m,function(){console.log("imgur rcvd: "+ (this.split("\n").length-1),--stack) });
};
function callback1(s){
  parse_page(s.toString());
  console.log(page,(new Date()-t1));
  if (--page>0) get_url("http://500px.com/"+tag+"?page="+page,function(){callback1(this.toString())})
  t1=new Date();
  }

callback1("");