server push in PHP

server-push.php

<?php 

  function push_to_browser($as, $uri) {
    header('Link: ' . $uri . '; rel=preload; as=' . $as, false);
  }

  $assets = array(
    // enter the path        enter the type of file (script / style / etc...)
    '<css/critical.css>' => 'style'
  );

  array_walk( $assets, 'push_to_browser');