Y.io() XDR requests make preflight OPTIONS request

[lsmith]

Posted for @chrisrhut, migrated from http://yuilibrary.com/projects/yui3/ticket/2533248

XDR requests on Chrome suddenly started making additional "preflight" OPTIONS requests in YUI 3.9.1. This line is the culprit:

// Convert falsy values to an empty string. This way IE can't be
// rediculous and translate `undefined` to "undefined".
data || (data = );

when the call is made to 'transaction.c.send(data);', Chrome adds the Content-Length: 0 header which, since it's not one of the "Simple" headers defined by the W3C (http://www.w3.org/TR/cors/#simple-header) triggers a preflight OPTIONS request to ensure CORS is authorized.
One possible fix is to make the above change conditional, as in:

if (!SUPPORTS_CORS) {
    // Convert falsy values to an empty string. This way IE can't be
    // ridiculous and translate `undefined` to "undefined".
    data || (data = );
}

The above is confirmed to work with Chrome and Firefox, have not tested IE.

[lsmith]

This is a regression that occurred somewhere between 3.7.1 and 3.9.1.

[lsmith]

Per my trak comment, I would recommend forking on data and calling send() without an argument rather than dance about with "acceptable" values between implementations.

Mind you, this should also be validated against the IE content-length issue.