function prepareRequest() {

    var http_request = false;

    if (window.XMLHttpRequest) { // Mozilla, Safari,...
        http_request = new XMLHttpRequest();
        if (http_request.overrideMimeType) {
            // See note below about this line
        }
    } else if (window.ActiveXObject) { // IE
        try {
            http_request = new ActiveXObject("Msxml2.XMLHTTP");
        } catch (e) {
            try {
                http_request = new ActiveXObject("Microsoft.XMLHTTP");
            } catch (e) {}
        }
    }
    if (!http_request) {
        alert('Ошибка при создании XMLHTTP'); return false;
    }
    return http_request;
}

function jsonMakeRequest(url) 
{
    http_request = prepareRequest();
    http_request.onreadystatechange = function() {  
        if (http_request.readyState ==  4 ) {
            if (http_request.status ==  200 ) {
                alert(http_request.responseText);
            } else {
                alert('There was a problem with the request.');
                http_request.responseText = '';
            }
        }
    }
    
    http_request.open('GET', url);
    http_request.send(null);
    alert('jsonMakeRequest');
    
    return http_request.responseText;
}