如何创建引导下拉菜单每当我在输入框中按下数字5时，都会出现引导下拉菜单

<input type="text" id="inputBox" onkeyup="showDropdown(event)">
<div id="dropdownContainer"></div>

function showDropdown(event) {
  var input = event.target.value;
  var dropdownContainer = document.getElementById("dropdownContainer");
  
  // 清空下拉菜单容器
  dropdownContainer.innerHTML = "";
  
  // 当输入框中按下数字5时，显示下拉菜单
  if (input.includes("5")) {
    var dropdownList = document.createElement("ul");
    
    // 添加下拉菜单项
    var item1 = document.createElement("li");
    item1.textContent = "菜单项1";
    dropdownList.appendChild(item1);
    
    var item2 = document.createElement("li");
    item2.textContent = "菜单项2";
    dropdownList.appendChild(item2);
    
    // 将下拉菜单添加到容器中
    dropdownContainer.appendChild(dropdownList);
  }
}

#dropdownContainer {
  position: absolute;
  top: 30px;
  left: 0;
  width: 200px;
  background-color: #fff;
  border: 1px solid #ccc;
  box-shadow: 0 2px 4px rgba(0, 0, 0, 0.2);
}

ul {
  list-style-type: none;
  padding: 0;
  margin: 0;
}

li {
  padding: 10px;
  cursor: pointer;
}

li:hover {
  background-color: #f5f5f5;
}