body 样式修改时未定义问题

src/components/video/camp/campTest.js

@@ -149,6 +149,7 @@ class CampTest extends Component {
         data.answer_record = this.answerList;
         http.post(`${API.home}/m/aist/submit`, data).then((res) => {
             if(res.data.code === 200) {
+                this.body = document.getElementsByTagName('body')[0];
                 this.body.style.position = 'static';
                 this.props.history.push(`/campResolve?keshi_id=${this.keshi_id}&qid=${this.qid}`, {from: this.props.location.state.from})
             }else{