404 Handler for JS Files

404js.php

<?php
// # 404 Handler for JS in Dev Environment
//
// I kept stubbing my toe. Backbone can make it hard to notice that a file
// has returned a 404 unless you have the console open. This makes it much
// more noticeable.
//
// This is coupled with the .htaccess file entry:
//
//    RewriteCond %{REQUEST_FILENAME} !-f
//    RewriteRule ^(.*)\.js$ /404js.php [L]
//

// Write to the error log so that it apache knows what happened and we can
// continue to tail the logs/error_log
error_log(
  'File does not exist: ' . $_SERVER["REQUEST_URI"] .
  ', referer: ' . $_SERVER["HTTP_REFERER"],
  4
);

// Tell the browser what happened, and that we're sending out JS
header("Status: 404 Not Found");
header("Content-type: text/javascript");

// Show the user what's up.
?>
alert(
  "4 0 4   J S   E R R O R\n" +
  "=============================\n" +
  "<?php echo htmlspecialchars($_SERVER["REQUEST_URI"]); ?> was not found."
);
<?php

/* End of file 404js.php */