我有一些按钮，我需要在单击时打开一个红色按钮，并将旧的红色按钮变成灰色，我该怎么办？

<button id="oldButton" class="redButton">旧的红色按钮</button>
<button id="newButton" class="redButton">新的红色按钮</button>

.redButton {
  background-color: red;
  color: white;
}

.grayButton {
  background-color: gray;
  color: black;
}

var oldButton = document.getElementById("oldButton");
var newButton = document.getElementById("newButton");

oldButton.addEventListener("click", function() {
  oldButton.classList.remove("redButton");
  oldButton.classList.add("grayButton");
  newButton.classList.remove("grayButton");
  newButton.classList.add("redButton");
});