vant/packages/tab/src/tab.vue

<template>
  <div class="van-tab__pane" :class="classNames">
    <slot></slot>
  </div>
</template>

<script>
  export default {
    name: 'van-tab',
    props: {
      // 选项卡头显示文字
      title: {
        type: String,
        required: true
      },
      disabled: Boolean
    },
    data() {
      const nextIndex = this.$parent.tabs.length;
      this.$parent.tabs.push({
        title: this.title,
        disabled: this.disabled,
        index: nextIndex
      });

      return {
        key: nextIndex
      };
    },
    computed: {
      classNames() {
        return { 'van-tab__pane--select': this.key === this.$parent.curActive };
      }
    }
  };
</script>