rq_rsp XHR

function request(url, tagname) {
    var xhr = new XMLHttpRequest();

    xhr.open("GET", url, true);
    xhr.onreadystatechange = function() {
        if (xhr.readyState == 4 && xhr.status == 200) {
                if (xhr.responseText == null) console.log('null_rq');
                var doc = document.implementation.createHTMLDocument("tmp");
                doc.documentElement.innerHTML = xhr.responseText;
                console.log(doc.getElementById(tagname).innerText);
            }
        }
    xhr.send();
    return xhr.responseText;
}

chrome.runtime.onMessage.addListener(function(message, sender, sendResponse) {
    console.log(sender.tab.url);
    if (message.key == "info") {
        console.log('Recideved "' + message.key + '" in background');

        var i, recieved_data = JSON.stringify(message.data);

        //alert('RECIEVED:' + recieved_data);
        //save_result(recieved_data);
        var curr_page;
        var curr_url, mathnet_main_url = "http://mi.mathnet.ru/intf";
        var url2 = "http://www.mathnet.ru/php/archive.phtml?wshow=paper&jrnid=intf&paperid=";
        var url3 = "&option_lang=rus";
        var tagname = "citPaperAMSBIBID";
        for (i = 1; i < 5; i++) {
            curr_url = url2 + i + url3;
            curr_page = request(curr_url, tagname);
            if (curr_page == null) console.log('null');
            //alert(curr_page);
        }

    }
    if (message.key == "rq") {

    }
});