vue用 computed 方法生成 class 或者 style 字符串，插入到页面中

 <template>
      <!-- 支持 -->
      <view class="container" :class="computedClassStr"></view>
      <view class="container" :class="{active: isActive}"></view>
      <!-- 不支持 -->
      <view class="container" :class="computedClassObject"></view>
  </template>
  <script>
      export default {
          data () {
              return {
                  isActive: true
              }
          },
          computed: {
              computedClassStr () {
                  return this.isActive ? ‘active‘ : ‘‘
              },
              computedClassObject () {
                  return { active: this.isActive }
              }
          }
      }
  </script>