错误 ：

 1. script.js:153 Uncaught TypeError: Cannot set property 'display' of
    undefined
        at script.js:153
        at NodeList.forEach (<anonymous>)
        at HTMLSelectElement.filterTodo (script.js:150)

代码 ：

enter code here function filterTodo(e) {
let todos = todoList.childNodes;
todos.forEach(function(todo) {
  switch (e.target.value) {
    case "all":
      todo.style.display = "flex";
      break;
    case "completed":
      if (todo.classList.contains("completed")) {
        todo.style.display = "flex";
      } else {
        todo.style.display = "none";
      }
      break;
    case "uncompleted":
      if (!todo.classList.contains("completed")) {
        todo.style.display = "flex";
      } else {
        todo.style.display = "none";
      }
  }
 });
}