Single Page App - Checking connection using XMLHttpRequest

spa-CheckingConnectionUsingXMLHttpRequest.js

function check() {
    var z, xml = null;
    xml = new XMLHttpRequest();
    // use xmlHttp object shown in the next snippet if you need to support IE6
    // xml = new xmlHttp
    xml.open("get", url, false);
    try {
        xml.send(null);
    } catch(z) {
        alert("Network failure");
        return;
    }
    if ((xml.status >= 200 && xml.status <= 300) || xml.status == 304) {
        var hi = xml.responseText;
    } else {
        alert("No Internet Connection! You will have to enter information by hand");
    }
}