noscript tag
<!--noscript is alternate content for people with scripts disabled in their browser-->
<head>
<noscript><style>h1{color:red;}</style></noscript><!--noscript in <head> can only have <link>, <style>, or <meta> elements-->
</head>
<body>
<script>document.body.innerHTML += "Hello, World!"</script>
<noscript>You do not have JavaScript enabled in your browser.</noscript>
</body>