Stages of XHR Request

xhrnotes.md

1. Create new XHRequest Object: var client = new XMLHttpRequest();
2. Assign handler to onreadystatechange event: client.onreadystatechange = handler;
3. This handler with normally check for a readyState of 4 and a status of 200

function handler() {
if(this.readyState == 4 && this.status == 200) {
// so far so good
if(this.responseXML != null && this.responseXML.getElementById('test').firstChild.data)
   // success!
 test(this.responseXML.getElementById('test').firstChild.data);
else
 test(null);
} else if (this.readyState == 4 && this.status != 200) {
// fetched the wrong page or network error...
test(null);
}
}

3. Open URL client.open("GET", "test.xml");
4. Send the request: client.send();

Source: https://www.w3.org/TR/2007/WD-XMLHttpRequest-20071026/