javascript - noob: how to show login error message on the same page after php server processes request

Question

I have a login page. User first enters information and submits the form.

And I have a php script that will see if the user exists.

If( authenticated == true)  
{  
    // I do a redirect  
}  
else  
{  
  // I want to popup an error message on the same page.  
} 

1) I'm not sure how to show the popup message, I would like to make my div element visible with an error message returned from the server,
I would have to use Ajax, right? But how?

Or are there alternatives which are just as good.

Answer 1

if you would use ajax, use it for the whole process. So, no such problems at all. Get response and show it to user.

But as you stated yourself as a newbie, I'd strongly advise you to do it straight and simple way, just to learn how the things are.

As a general rule, a redirect always preferred after POST method request. In some cases one can omit this, but for the login form you would use a session anyway. So, you can start a session, write an error information there and then do Location: redirect.

After it, check session for the errors, and then notify user using any method you wish: a div, or a popup or anything.