如果输入的前3个字符的值为"xyz“，如何禁用提交按钮并显示div

<input type="text" id="input" onkeyup="checkInput()" />
<button id="submit" disabled>提交</button>
<div id="message" style="display:none;">输入以xyz开头</div>

function checkInput() {
  var input = document.getElementById("input").value;
  var submit = document.getElementById("submit");
  var message = document.getElementById("message");

  if (input.substring(0, 3) === "xyz") {
    submit.disabled = false;
    message.style.display = "none";
  } else {
    submit.disabled = true;
    message.style.display = "block";
  }
}

#message {
  color: red;
  font-weight: bold;
}