1.4: xhr.readyState assignment crash (ajax.js line 461)

1.4: xhr.readyState assignment crash (ajax.js line 461)

 I have a question about code in ajax.js that is crashing for me in both FF and IE.

The code below starts on line 453 of th ajax.js module. -- (Note: In the released build this line ended-up at line number 4983 of jquery-1.4.js)

My questions are

1) Why the try {} around the function definition?

2) My crash is in the function at runtime, thus apparently not caught by the try{}

The offending line is #461

 (461)    xhr.readyState = 0;

The error as reported by the FireBug console: "setting a property that has only a getter".

All this smells fishy to me.  Anyone have insight to share?  When I comment-out that line everything works perfectly.

Here is a clip of the code in ajax.js starting at line #453

(453) // Override the abort handler, if we can (IE doesn't allow it, but that's OK)
        // Opera doesn't fire onreadystatechange at all on abort
        try {
            var oldAbort = xhr.abort;
            xhr.abort = function() {
                if ( xhr ) {
                    oldAbort.call( xhr );
                    if ( xhr ) {
                        xhr.readyState = 0;       // Boom!    

        } catch(e) { }

**--**  Steve