OL needs to support CORS and the HTTP 1.1 OPTIONS request method

[raj]

This particularly effects users who are trying to use jquery to access the OL API.

If you try to retrieve JSONP data using jquery's $.ajax(), $.getJSON() or related methods, jquery first makes a preflight request, as described in the CORS spec (http://www.w3.org/TR/cors/).

So a request for $.getJSON('http://openlibrary.org/books/OL1M.json?callback=foo') will first makes an OPTIONS request to that url, which will return a HTTP 405 error, which will cause the script to fail.

Workaround for jquery users:
If you use $.ajax() instead of $.getJSON() and set the dataType parameter to 'script', jquery will not make the OPTIONS request and just use the script src method to pull the data instead:

$.ajax({url: 'http://openlibrary.org/books/OL1M.json?callback=foo, dataType: 'script'});