// 1. create a new XMLHttpRequest object -- an object like any other!
var xhr = new XMLHttpRequest();
// 2. open the request and pass the HTTP method name and the resource as parameters
xhr.open('GET', 'file.html', true);
// 3. write a function that runs once the Ajax request resolves
xhr.onload = function () {
    // 4. check if the request is done and responded with success code
    if (xhr.readyState === xhr.DONE && xhr.status >= 200 && xhr.status < 300) {
        console.log(xhr.response);
        console.log(xhr.responseText);

        // 5. insert the text sent by the server into an HTML element with id="ajax-content"
        document.getElementById('ajax-content').innerHTML = xhr.responseText;
    }
};

var xhr = new XMLHttpRequest();
xhr.responseType = 'document';
xhr.open('GET', 'file.html', true);
xhr.onload = function () {
    if (xhr.readyState === xhr.DONE && xhr.status >= 200 && xhr.status < 300) {
        console.log(xhr.response);
        console.log(xhr.responseXML);

        // do stuff with xhr.responseXML...
    }
};