How does Crockford's json2.js libary support Graceful Degradation?

If an AJAX request made using jQuery fails,

Which statement is true for AJAX graceful degradation?

.................... stores a function (or the name of a function) to be called automatically each time the readyState property changes.

This __ event tells the browser to call the checkUsername() function when the user leaves the username field on the form.

Which is valid for addEventListener() method?

Which navigator properties is the same in both Netscape and IE?

In the following list, which ones are used to fetch the result data of an XMLHttpRequest?

Javascript uses static bindings.

Which describe the term 'Asynchronous' correctly?

Can you start multiple threads with JavaScript?