node.js sending POST requests not working

I'm trying to send a post request but It is not sending. I dont get output in the console log of the browser.

My node server.js is running in x.x.x.x:8000 then I connect it with my client.html. x.x.x.x:8000/client.html

Here is my node.js server.

function handler (req, res) {

  var filepath = '.' + req.url;
  if (filepath == './')
      filepath = './client.html';

  var extname = path.extname(filepath);
  var contentType = 'text/html';

  switch(extname){
    case '.js':
            contentType = 'text/javascript';
            break;
    case '.css':
            contentType = 'text/css';
            break;
  }

  path.exists(filepath, function (exists){
        if (exists){
            fs.readFile(filepath, function(error, content){
                if(error){
                    res.writeHead(500);
                    res.end();
                }
                else{
                    res.writeHead(200, { 'Content-Type': contentType });
                    res.end(content, 'utf-8');
                }
            });
        }
        else{
            res.writeHead(404);
            res.end();
        }
  });


}

JAVASCRIPT CODE - I'm using ajax call and sending request to COMMAND.php

 $.post( 
                '/var/www/COMMAND.php', 
                { cmd: "OUT" }, 
                function( data ){  

               console.log(data);



                });

PHP COMMAND.php - This writes to the the named pipe in linux. When it is done writing it echo success.

<?php

if ($_POST['cmd'] === 'OUT') {
    $con = fopen("/tmp/myFIFO", "w");
    fwrite($con, "OUT\n");
    fclose($con);
    echo "SUCCESS";
    exit;
}

?>

Why is it not sending any post requests to COMMAND.php? Is there any way for me to call COMMAND.php and execute the commands in it?