Ajax 手写JS

var httpRequest = false;
var mesdivs = null
function sendRequest(url, mesdiv) {
 
    mesdivs = mesdiv;
    httpRequest = false;
    if (window.XMLHttpRequest) {
        httpRequest = new XMLHttpRequest();
        if (httpRequest.overrideMimeType) {
        }
    }
    else if (window.ActiveXObject) {
        try {
            httpRequest = new ActiveXObject("Msxml2.XMLHTTP");
        }
        catch (e) {
            try {
                httpRequest = new ActiveXObject("Microsoft.XMLHTTP");
            }
            catch (e) {
            }
        }
    }
    if (!httpRequest) {
        window.alert("no");
    }
    if (mesdivs == "sendmes") {
        httpRequest.onreadystatechange = function() {
            if (httpRequest.readyState == 4) {
                if (httpRequest.status == 200) {
                    var string = httpRequest.responseText;
            &