Need info on json script

In the following code what is function(payload) doing??Actually i put an alert in function(payload){} i so not see the alert

EDIT

Also i see that there is a repose from the server but why is that i do not see an alert here

  $("form#form").submit(function(){
     $.post(url,
        {
          time: timestamp,
          action: "postmsg",
          message: $("#msg").val()
        },
        function(payload) {
          开发者_StackOverflowalert('1');
          $("#msg").val(""); // clean out contents of input field.
        },
        'json'
  );

Even with weird indentation I'm able to understand what's going on with my crazy JavaScript skills.

Your function(payload) is a callback to the $.post request. The callback will be called once the AJAX $.post request is done.

You probably don't see it run because url is returning a bad status code. The $.post callback will only run if the url is accessible with a correct status code.

For debugging try accessing url just from your browser, and see what happens.

It will run when the HTTP response comes back from the server

… unless the browser leaves the current page first, which it will do as the you aren't stopping the normal behaviour of the submit button.