看看这是否修复了它：

var LetsDoThis = document.querySelector("#toggle");
var LetsDoThat = document.querySelector("#content");

LetsDoThis.addEventListener("click", function({ currentTarget }) {
  // true if the class is added or false if it is removed
  let isOpen = LetsDoThat.classList.toggle("hidden");
  
  currentTarget.textContent = isOpen ? 'OPEN' : 'CLOSE'
});

.hidden {
  display: none;
}

<button id="toggle">OPEN</button>
<div id="content" class="hidden">
  When the "OPEN" button is clicked, the text must change from OPEN to CLOSE, all depending if it is open or closed
</div>

您可以通过检查按钮的文本来执行此操作：

var LetsDoThis = document.querySelector("#toggle");
var LetsDoThat = document.querySelector("#content");

LetsDoThis.addEventListener("click", function() {
  LetsDoThat.classList.toggle("hidden");
  (LetsDoThis.innerHTML == 'OPEN') ? LetsDoThis.innerHTML = 'CLOSED': LetsDoThis.innerHTML = 'OPEN';

});

.hidden {
  display: none;
}

<button id="toggle">OPEN</button>
<div id="content" class="hidden">
  When the "OPEN" button is clicked, the text must change from OPEN to CLOSE, all depending if it is open or closed
</div>

修改事件处理程序以包含按钮，如下所示。

LetsDoThis.addEventListener("click", function() {
  LetsDoThat.classList.toggle("hidden");
  LetsDoThis.innerText = LetsDoThis.innerText === "OPEN" ? "CLOSE" : "OPEN";
});