<!doctype html>
<html>
<head>
<meta charset="utf-8">
<style>
* { font-weight: bolder }
</style>
<script>
document.addEventListener("DOMContentLoaded", () => {
  document.querySelector("output").focus();
  document.execCommand("selectAll");
  document.execCommand("bold");
})
</script>
</head>
<body>
<output contenteditable="true">
A
</output></body>
</html>
