如何检测光标位置是否在richtextbox中的某些字符之间

// 获取光标位置
function getCaretPosition(element) {
  var caretPos = 0;
  if (document.selection) {
    // 兼容IE浏览器
    element.focus();
    var sel = document.selection.createRange();
    sel.moveStart('character', -element.value.length);
    caretPos = sel.text.length;
  } else if (element.selectionStart || element.selectionStart === '0') {
    // 兼容其他浏览器
    caretPos = element.selectionStart;
  }
  return caretPos;
}

// 检测光标位置是否在指定字符之间
function isCursorBetweenChars(element, startChar, endChar) {
  var text = element.value;
  var caretPos = getCaretPosition(element);
  
  // 判断光标前后的字符
  var charBeforeCursor = text.charAt(caretPos - 1);
  var charAfterCursor = text.charAt(caretPos);
  
  // 判断光标位置是否在指定字符之间
  if (charBeforeCursor === startChar && charAfterCursor === endChar) {
    return true;
  } else {
    return false;
  }
}

<textarea id="myTextarea"></textarea>

<script>
var textarea = document.getElementById('myTextarea');
textarea.addEventListener('keyup', function() {
  var isBetweenChars = isCursorBetweenChars(this, '[', ']');
  console.log(isBetweenChars);
});
</script>