Yet Another Salesforce REST API with JS

gistfile1.js

// refs: http://www.jitendrazaa.com/blog/salesforce/salesforce-rest-api-playground/
function getQueryStringValue (key) {  
  return unescape(window.location.search.replace(new RegExp("^(?:.*[&\\?]" + escape(key).replace(/[\.\+\*]/g, "\\$&") + "(?:\\=([^&]*))?)?.*$", "i"), "$1"));  
} 

{!REQUIRESCRIPT ("/soap/ajax/13.0/connection.js")};
var records = {!GETRECORDIDS($ObjectType.Book__c)};
var counter = 0;
for(var i=0; i<records.length; i++){
    var xmlhttp = new XMLHttpRequest();
    xmlhttp .onload = function(e) {
        counter++;
        if(counter === records.length) {
            var fcf = getQueryStringValue('fcf');
            var winlocation = window.location;
            window.open(winlocation.pathname + '/x?fcf='+fcf);
        }
    }
    xmlhttp.open("PATCH", '/services/data/v29.0/sobjects/Book__c/'+records[i], true);
    xmlhttp.setRequestHeader('Content-Type', 'application/json; charset=utf-8');
    xmlhttp.setRequestHeader('Authorization', 'Bearer {!$Api.Session_ID}');
    xmlhttp.send(JSON.stringify({IsPrinted__c:"true"}));
}

</script>

</apex:page>