var ajaxRequest = initAjaxRequest();

// initAjaxRequest(): Create a request object, based on browser type:

function initAjaxRequest() {
    var request;
        if (window.ActiveXObject) {
                request = new ActiveXObject("Microsoft.XMLHTTP");
        } else {
                request = new XMLHttpRequest();
        }
    return request;
}

// sendAjaxRequest(url, container): Send an asychronous request to a specific URL, designating CSS container ID to hold the response information (HTML).

function sendAjaxGetRequest(url, container) {
        ajaxRequest.open('GET', url);
        ajaxRequest.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");

    ajaxRequest.onreadystatechange = function() {
                if (ajaxRequest.readyState == 4 && ajaxRequest.status == 200) {
                        document.getElementById(container).innerHTML = ajaxRequest.responseText;
                }
        }
    ajaxRequest.send(null);
}

function sendAjaxPostRequest(url, parameters, container) {
    ajaxRequest.open('POST', url);
        ajaxRequest.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
    ajaxRequest.onreadystatechange = function() {
                if (ajaxRequest.readyState == 4 && ajaxRequest.status == 200) {
                        document.getElementById(container).innerHTML = ajaxRequest.responseText;
                }
        }
    ajaxRequest.send(parameters);
}