Web scripts that provide JSON responses are often invoked directly from
within a web browser by using the XMLHttpRequest object. This is a technique
popularly known as AJAX. For security reasons, solutions like these can run into cross-domain
issues, a restriction that requires you to proxy your requests on the server side. Typically,
to work around these issues, public services, such as Yahoo! JSON Services, provide a callback
mechanism.
Note: A full description of the JSON callback mechanism can be found at http://developer.yahoo.com/javascript/json.html#callbackparam on the
Yahoo! Developer Network.
Web scripts also provide this mechanism, which wraps the JSON response text in parentheses and a function name of your choosing. A callback is invoked by adding the following URL query parameter to the web script request:
- alf_callback=<function>
The function parameter specifies the name of a client-side JavaScript function to invoke.