Trying to execute shell command using javascript and php

Question

I am trying to execute shell command using JavaScript. I do not want to use a button to execute shell commands but a link (a href).

Below is the code I wanted to try:

<script type="text/javascript" src="jquery.min.js"></script> 
<script type="text/javascript"> 
function GPIO() 
{ 
  $.get("index.php"); 
       <?php
            $setmode17 = shell_exec("/usr/local/bin/gpio -g mode 17 out");
            $gpio_on = shell_exec("/usr/local/bin/gpio -g write 17 1");
       ?>
              return false; 
} 
    </script>

<a href="#" onclick="GPIO();">ON</a>