Question

What is the difference of these, and how do I know when to use which?

$.post($(this).attr('action'), $(this).serialize(), function(response) {
    // do something here on success
}, 'json');

$.post($(this).prop('action'), $(this).serialize(), function(response) {
    // do something here on success
}, 'json');

$.post($(this).closest("form").prop('action'), $(this).serialize(), function(response) {
    // do something here on success
}, 'json');

Answer 1

The first and second are identical, in this case. These functions has to be called from a form event handler. Instead of $(this).prop/attr(), $(this)[0].action and this.action can also be used.

The third method looks for the nearest form element, and retrieve the action attribute of the form. This method would be useful from a non-form context, e.g. from a button element.