Question

Today I am trying to echo this php mysql statement within my javascript code, which commences onclick. However, this php statement seems to run when the page loads on not wait until the onlclick event. Is there any way to solve this? I know that I could use javascript to open other pages and then call back the php statement, but I want this to be light weight.
Thanks!

<script type="text/javascript">
    function exitchatfriend() {
    document.getElementById("clicktoenteraconversation<?php 
                    echo $otherchatuser ?>").style.display='none';
    document.getElementById("chatcontainer").style.display='none';
    <?php mysql_query("DELETE FROM currentconversation 
            WHERE username='$username' and otherchatuser='$otherchatuser'"); ?>
    }
    </script>

Answer 1

You have a fundamental misunderstanding of the relative roles of PHP and javascript. PHP is a server-side will always execute before the page is sent to the client. This means that the code is never sent to the client, only the results. So if I have:

<?php echo "1+1 is ".(1+1); ?>

the source code that is sent to the client is

1+1 is 2

Javascript, on the other hand, is executed on the client’s side. The code is sent to the user’s computer, and you expect (hope) that the user’s browser correctly interprets the code and does what is being asked. (this is why javascript can’t be relied upon for validation, etc, as you can’t control what the client does with the code you send them).

If you want an onclick event to run a php script, you must use AJAX (which is basically just javascript executing a new page load in the background and doing something with the result). However, ajax is not super fast (you wouldn’t want to run

for(i=0;i<10000;i++){
   //some ajax call
}

and you can’t rely on it (so if it’s super important that this query gets run:

mysql_query("DELETE FROM currentconversation WHERE username='$username' and otherchatuser='$otherchatuser'");

you will want to look for other ways of closing the conversation.