Inspect the source code carefully and find where to inject :-)
<script src="hook.js"></script>
<script>
window.addEventListener("load", function() {
var q = location.hash.substring(1);
window.query.innerHTML = q == '' ? `Hello!` : (`Hello, ${decodeURI(q)}`);
});
</script>
<p id="query"></p>
<h1>inject</h1>
<p>Inspect the source code carefully and find where to inject :-)</p>
<h1>src</h1>
<?php highlight_string(file_get_contents(basename(__FILE__))); ?>