将javascript添加到php中的file_get_contents加载的html文件中

I am loading a html file by file_get_contents and make some changes over it and then echo it. I want to add a javascript code to the file but I don't know how to do it. Thanks in advance.

<?php
$page = file_get_contents('http://www.example.com/index.html');
$doc = new DOMDocument();
$doc->loadHTML($page);
$node = $doc->getElementById('something');
$node->parentNode->removeChild($node);
echo $doc->saveHtml($doc), PHP_EOL;
?>

<?php

$page = file_get_contents('http://example.com');
$doc = new DOMDocument();
$doc->loadHtml($page);

$head = $doc->getElementsByTagName("head")->item(0);

$js = $doc->createDocumentFragment();
$js->appendXml("<script> alert(1); </script>");
$head->appendChild($js);

echo $doc->saveHtml();

?>

This adds <script> alert(1); </script> to . Of course you can use "getElementById" and it be will exactly the same.

Hope this helps.