前置知识: JavaScript

JavaScript 项目示例：待办事项应用
00:00
3 min Intermediate
javascript project

综合运用 DOM 操作、事件处理与本地存储的待办事项应用。

完成任务点击切换完成状态，视觉反馈
删除任务删除单条任务，带确认和动画
编辑任务双击进入编辑模式
筛选任务全部/进行中/已完成
搜索任务实时搜索匹配
分类管理工作/学习/生活/其他
优先级高/中/低，颜色区分
数据持久化LocalStorage 自动保存和恢复
统计面板任务总数、完成率、各分类统计
拖拽排序拖拽调整任务顺序
批量操作全部完成/清除已完成

需求分析

数据需求

  • 每个任务包含：ID、标题、完成状态、优先级、分类、创建时间、完成时间
  • 数据存储在 LocalStorage 中，页面刷新不丢失
  • 支持最多 500 条任务

功能需求

  • 任务 CRUD 操作流畅
  • 筛选和搜索实时响应
  • 拖拽排序直观
  • 操作有动画反馈
  • 支持键盘快捷操作

非功能需求

  • 零依赖，纯原生实现
  • 响应式布局，适配移动端
  • 无障碍支持（ARIA 属性、键盘导航）

技术选型

技术点选型理由
DOM 操作原生 DOM API学习核心原理，不依赖框架
事件处理事件委托减少事件监听器数量，性能更优
数据存储LocalStorage简单持久化，无需后端
样式CSS3 + CSS 变量现代布局和动画
模板模板字符串简洁的 HTML 生成
状态管理发布-订阅模式解耦 UI 和数据逻辑

完整代码

HTML 结构

<!DOCTYPE html>
<html lang="zh-CN">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Todo App</title>
    <link rel="stylesheet" href="style.css" />
  </head>
  <body>
    <div class="app-container">
      <header class="app-header">
        <h1>Todo List</h1>
        <div class="stats-bar" id="statsBar"></div>
      </header>

      <div class="input-section">
        <form id="todoForm" class="todo-form">
          <input
            type="text"
            id="todoInput"
            class="todo-input"
            placeholder="What needs to be done?"
            autocomplete="off"
            required
          />
          <select id="prioritySelect" class="priority-select">
            <option value="medium">Medium</option>
            <option value="high">High</option>
            <option value="low">Low</option>
          </select>
          <select id="categorySelect" class="category-select">
            <option value="work">Work</option>
            <option value="study">Study</option>
            <option value="life">Life</option>
            <option value="other">Other</option>
          </select>
          <button type="submit" class="add-btn">Add</button>
        </form>
      </div>

      <div class="toolbar">
        <div class="filters">
          <button class="filter-btn active" data-filter="all">All</button>
          <button class="filter-btn" data-filter="active">Active</button>
          <button class="filter-btn" data-filter="completed">Completed</button>
        </div>
        <input type="text" id="searchInput" class="search-input" placeholder="Search tasks..." />
        <div class="batch-actions">
          <button id="completeAllBtn" class="batch-btn">Complete All</button>
          <button id="clearCompletedBtn" class="batch-btn">Clear Completed</button>
        </div>
      </div>

      <ul id="todoList" class="todo-list" role="list"></ul>

      <footer class="app-footer">
        <span id="itemCount"></span>
      </footer>
    </div>

    <script src="app.js"></script>
  </body>
</html>

CSS 样式

:root {
  --bg-primary: #f5f5f5;
  --bg-card: #ffffff;
  --text-primary: #333333;
  --text-secondary: #888888;
  --border-color: #e0e0e0;
  --accent: #4a90d9;
  --accent-hover: #357abd;
  --priority-high: #e74c3c;
  --priority-medium: #f39c12;
  --priority-low: #27ae60;
  --category-work: #3498db;
  --category-study: #9b59b6;
  --category-life: #1abc9c;
  --category-other: #95a5a6;
  --shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
  --radius: 8px;
  --transition: 0.3s ease;
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  background: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.6;
}

.app-container {
  max-width: 680px;
  margin: 40px auto;
  padding: 0 20px;
}

.app-header h1 {
  font-size: 2rem;
  font-weight: 300;
  text-align: center;
  color: var(--accent);
  margin-bottom: 8px;
}

.stats-bar {
  display: flex;
  justify-content: center;
  gap: 24px;
  font-size: 0.85rem;
  color: var(--text-secondary);
  margin-bottom: 20px;
}

.stats-bar .stat-value {
  font-weight: 600;
  color: var(--text-primary);
}

.todo-form {
  display: flex;
  gap: 8px;
  margin-bottom: 16px;
}

.todo-input {
  flex: 1;
  padding: 12px 16px;
  border: 2px solid var(--border-color);
  border-radius: var(--radius);
  font-size: 1rem;
  transition: border-color var(--transition);
  outline: none;
}

.todo-input:focus {
  border-color: var(--accent);
}

.priority-select,
.category-select {
  padding: 10px 12px;
  border: 2px solid var(--border-color);
  border-radius: var(--radius);
  font-size: 0.9rem;
  outline: none;
  cursor: pointer;
}

.add-btn {
  padding: 10px 20px;
  background: var(--accent);
  color: white;
  border: none;
  border-radius: var(--radius);
  font-size: 1rem;
  cursor: pointer;
  transition: background var(--transition);
}

.add-btn:hover {
  background: var(--accent-hover);
}

.toolbar {
  display: flex;
  align-items: center;
  gap: 12px;
  margin-bottom: 16px;
  flex-wrap: wrap;
}

.filters {
  display: flex;
  gap: 4px;
}

.filter-btn {
  padding: 6px 14px;
  border: 1px solid var(--border-color);
  border-radius: 20px;
  background: transparent;
  cursor: pointer;
  font-size: 0.85rem;
  transition: all var(--transition);
}

.filter-btn.active {
  background: var(--accent);
  color: white;
  border-color: var(--accent);
}

.search-input {
  flex: 1;
  min-width: 120px;
  padding: 8px 12px;
  border: 1px solid var(--border-color);
  border-radius: 20px;
  font-size: 0.85rem;
  outline: none;
}

.batch-btn {
  padding: 6px 12px;
  border: 1px solid var(--border-color);
  border-radius: var(--radius);
  background: transparent;
  cursor: pointer;
  font-size: 0.8rem;
  transition: all var(--transition);
}

.batch-btn:hover {
  background: var(--bg-primary);
}

.todo-list {
  list-style: none;
}

.todo-item {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 14px 16px;
  background: var(--bg-card);
  border-radius: var(--radius);
  margin-bottom: 8px;
  box-shadow: var(--shadow);
  transition: all var(--transition);
  cursor: grab;
}

.todo-item:hover {
  transform: translateY(-1px);
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
}

.todo-item.dragging {
  opacity: 0.5;
  transform: scale(0.98);
}

.todo-item.completed .todo-text {
  text-decoration: line-through;
  color: var(--text-secondary);
}

.todo-checkbox {
  width: 22px;
  height: 22px;
  border: 2px solid var(--border-color);
  border-radius: 50%;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all var(--transition);
  flex-shrink: 0;
}

.todo-checkbox.checked {
  background: var(--accent);
  border-color: var(--accent);
}

.todo-checkbox.checked::after {
  content: '';
  width: 6px;
  height: 10px;
  border: solid white;
  border-width: 0 2px 2px 0;
  transform: rotate(45deg) translate(-1px, -1px);
}

.todo-text {
  flex: 1;
  font-size: 0.95rem;
  word-break: break-word;
}

.todo-text-edit {
  flex: 1;
  font-size: 0.95rem;
  padding: 4px 8px;
  border: 1px solid var(--accent);
  border-radius: 4px;
  outline: none;
}

.priority-badge {
  padding: 2px 8px;
  border-radius: 10px;
  font-size: 0.7rem;
  font-weight: 600;
  text-transform: uppercase;
}

.priority-high {
  background: #fde8e8;
  color: var(--priority-high);
}
.priority-medium {
  background: #fef3cd;
  color: var(--priority-medium);
}
.priority-low {
  background: #d4edda;
  color: var(--priority-low);
}

.category-tag {
  padding: 2px 8px;
  border-radius: 10px;
  font-size: 0.7rem;
  background: var(--bg-primary);
  color: var(--text-secondary);
}

.category-work {
  color: var(--category-work);
}
.category-study {
  color: var(--category-study);
}
.category-life {
  color: var(--category-life);
}
.category-other {
  color: var(--category-other);
}

.delete-btn {
  background: none;
  border: none;
  color: var(--text-secondary);
  cursor: pointer;
  font-size: 1.2rem;
  padding: 4px 8px;
  border-radius: 4px;
  transition: all var(--transition);
  opacity: 0;
}

.todo-item:hover .delete-btn {
  opacity: 1;
}

.delete-btn:hover {
  color: var(--priority-high);
  background: #fde8e8;
}

.app-footer {
  text-align: center;
  padding: 16px 0;
  color: var(--text-secondary);
  font-size: 0.85rem;
}

@keyframes slideIn {
  from {
    opacity: 0;
    transform: translateY(-10px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes slideOut {
  from {
    opacity: 1;
    transform: translateX(0);
  }
  to {
    opacity: 0;
    transform: translateX(30px);
  }
}

.todo-item.entering {
  animation: slideIn 0.3s ease forwards;
}
.todo-item.leaving {
  animation: slideOut 0.3s ease forwards;
}

@media (max-width: 600px) {
  .todo-form {
    flex-wrap: wrap;
  }
  .todo-input {
    min-width: 100%;
  }
  .toolbar {
    flex-direction: column;
    align-items: stretch;
  }
  .batch-actions {
    display: flex;
    gap: 8px;
  }
}

JavaScript 核心逻辑

const TodoApp = (function () {
  const STORAGE_KEY = 'todo_app_data';
  let todos = [];
  let currentFilter = 'all';
  let searchQuery = '';
  let dragItem = null;

  const pubsub = {
    events: {},
    on(event, callback) {
      if (!this.events[event]) this.events[event] = [];
      this.events[event].push(callback);
    },
    emit(event, data) {
      if (this.events[event]) {
        this.events[event].forEach((cb) => cb(data));
      }
    },
  };

  function generateId() {
    return Date.now().toString(36) + Math.random().toString(36).slice(2, 8);
  }

  function loadTodos() {
    try {
      const data = localStorage.getItem(STORAGE_KEY);
      todos = data ? JSON.parse(data) : [];
    } catch (e) {
      console.error('Failed to load todos:', e);
      todos = [];
    }
  }

  function saveTodos() {
    try {
      localStorage.setItem(STORAGE_KEY, JSON.stringify(todos));
    } catch (e) {
      console.error('Failed to save todos:', e);
    }
  }

  function addTodo(title, priority, category) {
    const todo = {
      id: generateId(),
      title: title.trim(),
      completed: false,
      priority: priority || 'medium',
      category: category || 'other',
      createdAt: new Date().toISOString(),
      completedAt: null,
    };
    todos.unshift(todo);
    saveTodos();
    pubsub.emit('todo:added', todo);
    pubsub.emit('todo:changed');
    return todo;
  }

  function toggleTodo(id) {
    const todo = todos.find((t) => t.id === id);
    if (!todo) return;
    todo.completed = !todo.completed;
    todo.completedAt = todo.completed ? new Date().toISOString() : null;
    saveTodos();
    pubsub.emit('todo:toggled', todo);
    pubsub.emit('todo:changed');
  }

  function deleteTodo(id) {
    const index = todos.findIndex((t) => t.id === id);
    if (index === -1) return;
    const removed = todos.splice(index, 1)[0];
    saveTodos();
    pubsub.emit('todo:deleted', removed);
    pubsub.emit('todo:changed');
  }

  function updateTodo(id, updates) {
    const todo = todos.find((t) => t.id === id);
    if (!todo) return;
    Object.assign(todo, updates);
    saveTodos();
    pubsub.emit('todo:updated', todo);
    pubsub.emit('todo:changed');
  }

  function getFilteredTodos() {
    return todos.filter((todo) => {
      const matchesFilter =
        currentFilter === 'all' ||
        (currentFilter === 'active' && !todo.completed) ||
        (currentFilter === 'completed' && todo.completed);

      const matchesSearch =
        !searchQuery || todo.title.toLowerCase().includes(searchQuery.toLowerCase());

      return matchesFilter && matchesSearch;
    });
  }

  function completeAll() {
    const activeTodos = todos.filter((t) => !t.completed);
    activeTodos.forEach((t) => {
      t.completed = true;
      t.completedAt = new Date().toISOString();
    });
    saveTodos();
    pubsub.emit('todo:changed');
  }

  function clearCompleted() {
    todos = todos.filter((t) => !t.completed);
    saveTodos();
    pubsub.emit('todo:changed');
  }

  function reorderTodos(fromIndex, toIndex) {
    const filtered = getFilteredTodos();
    const movedTodo = filtered[fromIndex];
    const targetTodo = filtered[toIndex];
    const realFrom = todos.findIndex((t) => t.id === movedTodo.id);
    const realTo = todos.findIndex((t) => t.id === targetTodo.id);
    todos.splice(realFrom, 1);
    todos.splice(realTo, 0, movedTodo);
    saveTodos();
    pubsub.emit('todo:changed');
  }

  function getStats() {
    const total = todos.length;
    const completed = todos.filter((t) => t.completed).length;
    const active = total - completed;
    const rate = total > 0 ? Math.round((completed / total) * 100) : 0;
    const byCategory = {};
    todos.forEach((t) => {
      byCategory[t.category] = (byCategory[t.category] || 0) + 1;
    });
    return { total, completed, active, rate, byCategory };
  }

  function renderTodoItem(todo) {
    const li = document.createElement('li');
    li.className = `todo-item${todo.completed ? ' completed' : ''} entering`;
    li.dataset.id = todo.id;
    li.setAttribute('draggable', '');
    li.setAttribute('role', 'listitem');

    li.innerHTML = `
            <div class="todo-checkbox${todo.completed ? ' checked' : ''}"
                 role="checkbox" aria-checked="${todo.completed}"
                 tabindex="0" aria-label="Toggle completion"></div>
            <span class="todo-text">${escapeHtml(todo.title)}</span>
            <span class="priority-badge priority-${todo.priority}">${todo.priority}</span>
            <span class="category-tag category-${todo.category}">${todo.category}</span>
            <button class="delete-btn" aria-label="Delete task">&times;</button>
        `;

    setTimeout(() => li.classList.remove('entering'), 300);
    return li;
  }

  function escapeHtml(str) {
    const div = document.createElement('div');
    div.textContent = str;
    return div.innerHTML;
  }

  function renderList() {
    const list = document.getElementById('todoList');
    list.innerHTML = '';
    const filtered = getFilteredTodos();
    filtered.forEach((todo) => {
      list.appendChild(renderTodoItem(todo));
    });
  }

  function renderStats() {
    const stats = getStats();
    document.getElementById('statsBar').innerHTML = `
            <span>Total: <span class="stat-value">${stats.total}</span></span>
            <span>Active: <span class="stat-value">${stats.active}</span></span>
            <span>Done: <span class="stat-value">${stats.completed}</span></span>
            <span>Rate: <span class="stat-value">${stats.rate}%</span></span>
        `;
    document.getElementById('itemCount').textContent =
      `${stats.active} item${stats.active !== 1 ? 's' : ''} left`;
  }

  function initEventListeners() {
    const form = document.getElementById('todoForm');
    const list = document.getElementById('todoList');
    const searchInput = document.getElementById('searchInput');

    form.addEventListener('submit', function (e) {
      e.preventDefault();
      const input = document.getElementById('todoInput');
      const priority = document.getElementById('prioritySelect').value;
      const category = document.getElementById('categorySelect').value;
      if (input.value.trim()) {
        addTodo(input.value, priority, category);
        input.value = '';
        input.focus();
      }
    });

    list.addEventListener('click', function (e) {
      const item = e.target.closest('.todo-item');
      if (!item) return;
      const id = item.dataset.id;

      if (e.target.closest('.todo-checkbox')) {
        toggleTodo(id);
      } else if (e.target.closest('.delete-btn')) {
        item.classList.add('leaving');
        setTimeout(() => deleteTodo(id), 300);
      }
    });

    list.addEventListener('dblclick', function (e) {
      const item = e.target.closest('.todo-item');
      if (!item) return;
      const textEl = e.target.closest('.todo-text');
      if (!textEl) return;

      const id = item.dataset.id;
      const todo = todos.find((t) => t.id === id);
      if (!todo || todo.completed) return;

      const input = document.createElement('input');
      input.type = 'text';
      input.className = 'todo-text-edit';
      input.value = todo.title;

      textEl.replaceWith(input);
      input.focus();
      input.select();

      function finishEdit() {
        const newTitle = input.value.trim();
        if (newTitle && newTitle !== todo.title) {
          updateTodo(id, { title: newTitle });
        }
        renderList();
      }

      input.addEventListener('blur', finishEdit);
      input.addEventListener('keydown', function (e) {
        if (e.key === 'Enter') input.blur();
        if (e.key === 'Escape') {
          input.value = todo.title;
          input.blur();
        }
      });
    });

    list.addEventListener('keydown', function (e) {
      if (e.key === 'Enter' || e.key === ' ') {
        const checkbox = e.target.closest('.todo-checkbox');
        if (checkbox) {
          e.preventDefault();
          const item = checkbox.closest('.todo-item');
          toggleTodo(item.dataset.id);
        }
      }
    });

    document.querySelector('.filters').addEventListener('click', function (e) {
      const btn = e.target.closest('.filter-btn');
      if (!btn) return;
      document.querySelectorAll('.filter-btn').forEach((b) => b.classList.remove('active'));
      btn.classList.add('active');
      currentFilter = btn.dataset.filter;
      renderList();
    });

    searchInput.addEventListener('input', function () {
      searchQuery = this.value;
      renderList();
    });

    document.getElementById('completeAllBtn').addEventListener('click', completeAll);
    document.getElementById('clearCompletedBtn').addEventListener('click', clearCompleted);

    list.addEventListener('dragstart', function (e) {
      dragItem = e.target.closest('.todo-item');
      if (dragItem) {
        dragItem.classList.add('dragging');
        e.dataTransfer.effectAllowed = 'move';
      }
    });

    list.addEventListener('dragover', function (e) {
      e.preventDefault();
      const afterElement = getDragAfterElement(list, e.clientY);
      if (afterElement) {
        list.insertBefore(dragItem, afterElement);
      } else {
        list.appendChild(dragItem);
      }
    });

    list.addEventListener('dragend', function () {
      if (dragItem) {
        dragItem.classList.remove('dragging');
        const items = [...list.querySelectorAll('.todo-item')];
        const fromIndex = getFilteredTodos().findIndex((t) => t.id === dragItem.dataset.id);
        const toIndex = items.findIndex((el) => el.dataset.id === dragItem.dataset.id);
        if (fromIndex !== toIndex && fromIndex !== -1 && toIndex !== -1) {
          reorderTodos(fromIndex, toIndex);
        }
        dragItem = null;
      }
    });

    pubsub.on('todo:changed', function () {
      renderList();
      renderStats();
    });
  }

  function getDragAfterElement(container, y) {
    const elements = [...container.querySelectorAll('.todo-item:not(.dragging)')];
    return elements.reduce(
      (closest, child) => {
        const box = child.getBoundingClientRect();
        const offset = y - box.top - box.height / 2;
        if (offset < 0 && offset > closest.offset) {
          return { offset, element: child };
        }
        return closest;
      },
      { offset: Number.NEGATIVE_INFINITY }
    ).element;
  }

  function init() {
    loadTodos();
    initEventListeners();
    renderList();
    renderStats();
  }

  return { init };
})();

document.addEventListener('DOMContentLoaded', TodoApp.init);

运行说明

直接打开

将 HTML、CSS 和 JS 文件放在同一目录，用浏览器打开 HTML 文件即可。

文件结构

todo-app/
  index.html
  style.css
  app.js

数据存储

  • 数据自动保存在浏览器的 LocalStorage 中
  • 键名：todo_app_data
  • 清除数据：浏览器开发者工具 -> Application -> Local Storage -> 删除对应键

扩展方向

  1. 截止日期 — 添加任务截止日期，超期提醒
  2. 子任务 — 支持任务嵌套子任务
  3. 标签系统 — 自定义标签替代固定分类
  4. 导入导出 — JSON 格式导入导出任务数据
  5. 暗色模式 — CSS 变量切换主题
  6. PWA — 添加 Service Worker 支持离线使用
  7. 后端同步 — 接入 REST API 实现多设备同步

关键代码速查

LocalStorage 操作

localStorage.setItem('key', JSON.stringify(data));
const data = JSON.parse(localStorage.getItem('key'));
localStorage.removeItem('key');

事件委托

list.addEventListener('click', function (e) {
  const item = e.target.closest('.todo-item');
  if (!item) return;
  const id = item.dataset.id;
  if (e.target.closest('.delete-btn')) {
    /* ... */
  }
});

DOM 创建元素

const li = document.createElement('li');
li.className = 'todo-item';
li.dataset.id = id;
li.innerHTML = `<span class="text">${title}</span>`;
list.appendChild(li);

拖拽排序

element.addEventListener('dragstart', (e) => {
  /* 记录拖拽项 */
});
element.addEventListener('dragover', (e) => {
  e.preventDefault(); /* 插入位置 */
});
element.addEventListener('drop', (e) => {
  /* 重新排序 */
});

发布订阅模式

const pubsub = {
  events: {},
  on(event, cb) {
    (this.events[event] ||= []).push(cb);
  },
  emit(event, data) {
    (this.events[event] || []).forEach((cb) => cb(data));
  },
};

CSS 动画

@keyframes slideIn {
  from {
    opacity: 0;
    transform: translateY(-10px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}
.todo-item.entering {
  animation: slideIn 0.3s ease forwards;
}

知识检测

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