add onclick function to a submit button

I need to see your submit button html tag for better help. I am not familiar with php and how it handles the postback, but I guess depending on what you want to do, you have three options:

1. Getting the handling onclick button on the client-side: In this case you only need to call a javascript function.

function foo() {
   alert("Submit button clicked!");
   return true;
}

<input type="submit" value="submit" onclick="return foo();" />

2. If you want to handle the click on the server-side, you should first make sure that the form tag method attribute is set to post:

   <form method="post">
   

3. You can use onsubmit event from form itself to bind your function to it.

<form name="frm1" method="post" onsubmit="return greeting()">
    <input type="text" name="fname">
    <input type="submit" value="Submit">
</form>