AJAX - The Complete Reference

Chapter 3: XMLHttpRequest Object 63

PART I

Property or Method Description

open(method, url [,

asynchronous [, user,

password]])

Initializes the request in preparation for sending to the

ser ver. The method parameter is the HTTP method to use,

for example “GET” or “POST”. The value of method is not

case sensitive. The url is the relative or absolute URL the

request will be sent to. The optional asynchronous parameter

indicates whether send() returns immediately or after the

request is complete (default is true, meaning it returns

immediately). The optional user and password arguments are

to be used if the URL requires HTTP authentication. If none

are specified and the URL requires authentication, the user

will be prompted to enter it

setRequestHeader(name,

value)

Adds the HTTP header given by the name (without the colon)

and value parameters

send(body) Initiates the request to the ser ver. The body parameter

should contain the body of the request, i.e., a string

containing fieldname=value&fieldname2=value2... for POSTs

or a null value for GET request

TABLE 3-2 Common Properties and Methods of the XMLHttpRequest Object (continued)

Property or Method Description Browser Support

onload Event triggered when whole

document has finished

loading, similar to looking at

onreadystatechange when

the readyState value is 4.

Firefox 1.5+

onprogress Event triggered as partial

data becomes available. The

event will fire continuously

as data is made available.

Firefox 1.5+

onerror Event triggered when a

network error occurs.

Firefox 1.5+ (still buggy

as of Firefox 2)

overrideMimeType(‘mime-type’) Method takes a string for a

MIME type value (e.g., text/

xml) and overrides whatever

MIME type is indicated in the

response packet.

Firefox 1.5+, Opera

(buggy)

TABLE 3-3 Browser-specific XHR Properties and Methods