286653 - Passing parameters to XMLHttpRequest.onreadystatechange callback breaks scripts

Status: RESOLVED INVALID

(Core :: DOM: UI Events & Focus Handling, defect)

Description

[Michael Newton]

User-Agent:       Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.6) Gecko/20050225 Firefox/1.0.1
Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.6) Gecko/20050225 Firefox/1.0.1

Using the basic Apple XMLHttpRequest example at
http://developer.apple.com/internet/webcontent/xmlhttpreq.html as a template, I
was trying to pass a variable to the onreadystatechange callback function, like so:

req=new XMLHttpRequest;
req.onreadystatechange=processReqChange(foo);

This would not work.  Some debugging in processReqChange determined that
req.readyState was not advancing beyond 0 (uninitialized.)  Simply removing the
parameter foo from the callback declaration fixed it up just fine and let
req.readyState advance all the way to 4:

req=new XMLHttpRequest;
req.onreadystatechange=processReqChange;

I couldn't find any formal documentation on XMLHttpRequest, so I'm not entirely
sure if this is the wrong way to do it, but it seemed like a bug to me.

A fairly simple workaround is to pass the data into the PHP script as a GET
variable and have it spit it out in the XML data.

Reproducible: Always

Steps to Reproduce:

Comment 1

[Bob Clary [:bc] (inactive)]

req.onreadystatechange=processReqChange(foo) does not assign a reference to the
function processReqChange to req.onreadystatechange but instead calls
processReqChange with argument foo and assigns the return value to
reg.onreadystatechange. 

Without a testcase, I would be inclined to mark this invalid. Please attach your
example using "Create a New Attachment" link.

Comment 2

[Michael Newton]

Ok, didn't realize that the function would actually be called, and it's value
returned.  I was thinking, as you said, that it was assigning a reference. 
Sorry for the bugspam!