data() {
      return {
        //已经选择的题目id集合
        selectQuestionIdArrayList: [],
      }

components: {
      QuestionForTestPaper
    },

<QuestionForTestPaper v-bind:selectQuestionIdArrayList="selectQuestionIdArrayList"
          ></QuestionForTestPaper>

export default {
    name: 'index',
    props: ['selectQuestionIdArrayList'],
//监听数据变化
    watch: {
      selectQuestionIdArrayList: function(newVal, oldVal) {
      //将数据赋值给子组件的变量
        this.selectQuestionIdList = newVal
        console.log('this.selectQuestionIdList>>' + this.selectQuestionIdList)
      }
    },
……
  }