Hacking Gmail

60 Part II — Getting Inside Gmail

Table 5-1(continued)

Method Description

getResponseHeader(“headerLabel”) Returns the string value of a single header

label.

open(“method”, “URL”[, asyncFlag[, Assigns the method, the URL, and the other

“userName”[, “password”]]]) optional attributes of a pending request.

send(content) Sends the request, with an optional postable

string or bit of DOM object data.

setRequestHeader(“label”, “value”) Assigns a label/value pair to the header to be

sent with a request.

Table 5-2 contains some of the XMLHttpRequestobject properties you’ll likely

need to use.

Table 5-2 Common XMLHttpRequest Object Properties

Property Description

onreadystatechange Event handler for an event. It fires whenever the state changes.

readyState Object status integer:

0 = uninitialized

1 = loading

2 = loaded

3 = interactive

4 = complete

responseText The data returned from the server, as a string.

responseXML The data returned from the server, as a DOM-compatible

document object.

status Numeric http status code returned by server, such as 404 for

“Not Found” or 200 for “OK.”

statusText Any string message accompanying the status code.

You should now feel confident that you understand how a simple HTML and

JavaScript document can request data from a server in the background. There’s no

need for the page to reload in the browser for you to retrieve new information.