HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>queryCommandEnabled SelectAll</title>
  <style>body{font-family:system-ui,sans-serif;margin:1rem;}#box{border:1px solid #ccc;padding:0.75rem;min-height:3rem;}</style>
</head>
<body>
  <div id="box" contenteditable="true">Select this text with SelectAll</div>
  <pre id="out"></pre>
  <script>
    var lines = [];
    var flg = typeof document.queryCommandEnabled === "function"
      ? document.queryCommandEnabled("SelectAll")
      : false;
    lines.push("SelectAll enabled: " + flg);
    if (flg) {
      document.execCommand("SelectAll", false, null);
      lines.push("SelectAll ran");
    }
    document.getElementById("out").textContent = lines.join("\n");
  </script>
</body>
</html>

Lines: 0 | Characters: 0

Live Preview Auto-refresh on Run

Document.queryCommandEnabled — SelectAll then execCommand (Try It)