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<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<script>
document.addEventListener("DOMContentLoaded", function() {
const input = document.querySelector("input[name='author']"),
author = localStorage.getItem("commenter_author");
if (author) input.value = author
input.addEventListener("input", function() {
localStorage.setItem("commenter_author", input.value)
})
});
</script>
</head>
<body>
<input type="text" name="author">
</body>
</html>