<!DOCTYPE html>
<html>
<body>
<form>
<input type="button" id="btn01" value="OK">
</form>
<p>Click the "Disable" button to disable the "OK" button:</p>
<button onclick="disableElement()">Disable</button>
<script>
function disableElement() {
document.getElementById("btn01").disabled = true;
}
</script>
</body>
</html>