回答

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">

  <style>
    body {
      margin: 0;
      padding: 20px;
      font-family: Arial, sans-serif;
      transition: background-color 0.3s ease;
    }

    .file-drop {
      border: 2px dashed #ccc;
      padding: 20px;
      text-align: center;
      cursor: pointer;
    }

    .file-drop:hover {
      background-color: #f0f0f0;
    }

    .file-list {
      margin-top: 20px;
    }

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

    .file-list li {
      margin-bottom: 5px;
    }
  </style>
</head>
<body>
  <div id="app">
    <div class="file-drop" v-if="!file">
      <p>拖拽单个文件到这里 (仅限 .jpg 和 .png 文件)</p>
    </div>
    <div class="file-list" v-else>
      <ul>
        <li>
          {{ file.name }} ({{ file.size }} bytes)
        </li>
      </ul>
    </div>
  </div>

  <!-- 引入 Vue 2 CDN -->
<script type="text/javascript" src="//repo.bfw.wiki/bfwrepo/js/vue@2.6.1-dev.js"></script>

  <script>
    new Vue({
      el: '#app',
      data() {
        return {
          file: null
        };
      },
      methods: {
        handleDragOver(event) {
          event.preventDefault();
          document.body.style.backgroundColor = '#e0f7fa'; // 拖动时改变背景颜色
        },
        handleDragLeave() {
          document.body.style.backgroundColor = ''; // 拖动离开时恢复背景颜色
        },
        handleDrop(event) {
          event.preventDefault();
          document.body.style.backgroundColor = ''; // 放开时恢复背景颜色
          const files = event.dataTransfer.files;
          if (files.length === 1) {
            const file = files[0];
            const allowedTypes = ['image/jpeg', 'image/png'];
            if (allowedTypes.includes(file.type)) {
              this.file = file;
            } else {
              alert('只能拖拽 .jpg 和 .png 文件');
            }
          } else {
            alert('只能拖拽单个文件');
          }
        }
      },
      mounted() {
        document.body.addEventListener('dragover', this.handleDragOver);
        document.body.addEventListener('dragleave', this.handleDragLeave);
        document.body.addEventListener('drop', this.handleDrop);
      },
      beforeDestroy() {
        document.body.removeEventListener('dragover', this.handleDragOver);
        document.body.removeEventListener('dragleave', this.handleDragLeave);
        document.body.removeEventListener('drop', this.handleDrop);
      }
    });
  </script>
</body>
</html>