JavaScript で関数のクロージャにプログラム的にアクセスできますか?

<code class="js">var x = (function(){
   var y = 5;
   return function() {
       alert(y);
   };
})();

//access y here with x somehow</code>

<code class="js">new MutationObserver((mutations, observer) => {
  // Find the target script tag
  const tamperTarget = document.querySelector('script + script');
  if (!tamperTarget) {
    return;
  }
  observer.disconnect();
  console.log('Target script getting tampered with');

  // Modify the script's content to expose the closure
  tamperTarget.textContent = tamperTarget.textContent.replace(
    'return function',
    'window.y = y; return function'
  );

  setTimeout(() => {
    console.log("Hacked into tamper target's script and found a y of", y);
    console.log('Could also have replaced the local y with another value');
  });
})
  .observe(document.body, { childList: true });</code>