Re: ISSUE-101: Network errors for sync requests

To be able to report network errors in a consistent way for asynchronous and
synchronous requests, XHR could make use of deferred exceptions for the
async case (assuming that sync requests will continue to throw NETWORK_ERR
in future specs).
 
This could be done by letting all properties that are results of the
response throw a deferred NETWORK_ERR. Thus, a client script that sends an
asynchronous XHR request and doesn't check on the response's status or
content will not encounter the exception (which makes sense as it apparently
isn't interested in the result).
But a script checking response status or content will have the correct
exception thrown at inspection time. See example below, where a network
error would cause a deferred exception to be thrown at the test for
"this.status == 200".
 
function handler() {
    if (this.readyState == 4) {
        try {
            if (this.status == 200) {
                ...
            }
        }
        catch(netErr) {
            ...
        }
}
var client = new XMLHttpRequest();
client.onreadystatechange = handler;
client.open("GET", "test.xml");
client.send();
 
This would offer a similar solution for async requests as for the synced,
and throws exceptions at a point where they may be caught instead of going
straight into the global error handler, which has been discussed as a
problem earlier on.
 
Best regards
Mike Wilson