[jQuery] ajax api question

[james_027]

Hi,

I am using $.post() function, I don't understand what is callback
function ...

what is the difference between

$.post('test.cgi', params,
    function(data) {
        alert(data);
    }
);

and

$.post('test.cgi', params, alert(data));

the data being shown is different. and I don't seem to understand what
is the difference in function(data) {alert(data);} from alert(data).
For me function(data) {alert(data);} is just a function taking the
data and just passing it to the alert(). Is function() inside the
$.post something special? where does the data come from? are the data
in the function(data) {alert(data);} and alert(data) different?

Thanks
james