HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>execCommand bold</title>
  <style>body{font-family:system-ui,sans-serif;padding:1.5rem;} #editor{border:1px solid #ccc;padding:0.75rem;min-height:4rem;margin:0.75rem 0;} pre{border:1px solid #ccc;padding:0.75rem;}</style>
</head>
<body>
  <p>Select some text below, then click Bold.</p>
  <div id="editor" contenteditable="true">Hello <strong>world</strong> — try selecting me.</div>
  <button id="btn" type="button">Bold</button>
  <pre id="out">Click Bold after selecting text</pre>
  <script>
    document.getElementById("btn").addEventListener("click", function () {
      document.getElementById("editor").focus();
      var ok = document.execCommand("bold", false, null);
      document.getElementById("out").textContent = ok
        ? "bold toggled"
        : "bold failed / unsupported";
    });
  </script>
</body>
</html>

Lines: 0 | Characters: 0

Live Preview Auto-refresh on Run

Document.execCommand — bold (Try It)