如何使用javascript更改文本区域字段的值以触发按钮禁用更改？

var textarea = document.getElementById("myTextarea");

textarea.value = "新的文本值";

var button = document.getElementById("myButton");
button.disabled = true;

<textarea id="myTextarea"></textarea>
<button id="myButton">按钮</button>

<script>
  var textarea = document.getElementById("myTextarea");
  textarea.value = "新的文本值";

  var button = document.getElementById("myButton");
  button.disabled = true;
</script>