Executar método de comando

<!DOCTYPE html>
<html>
<body onkeydown="myFunction(event)">

<h1>The Document Object</h1>
<h2>The execCommand() Method</h2>

<p>The executeCommand() method executes a specified command on selected text.</p>
<p>Select some text in this page, and press SHIFT to make the selected text toggle between bold and normal.</p>

<script>
document.designMode = "on";

function myFunction(event) {
  if (event.keyCode == 16) {
    // Execute command if user presses the SHIFT button:
    document.execCommand("bold");
  }
}

</script>

</body>
</html>
ayaan