javascript - 收到预期赋值或函数调用却看到表达式 no-unused-expressions 的错误？

Question

我是 React js 新手，正在学习 Udemy 类(class)，但收到错误消息“预期分配或函数调用，而是看到表达式 no-unused-expressions”。基本上，我正在使用 firebase 数据库来在此应用程序中开发此应用程序，用户将自己的名字设为学生。

import React, { Component } from 'react';
import 'bootstrap/dist/css/bootstrap.min.css';

var firebase=require('firebase');
var uuid=require('uuid');

var firebaseConfig = {
    apiKey: "AIzaSyAwXf9-4PgY0ttsGy1FHmyLHZOFO1oVcic",
    authDomain: "uservey-206d4.firebaseapp.com",
    databaseURL: "https://uservey-206d4.firebaseio.com",
    projectId: "uservey-206d4",
    storageBucket: "uservey-206d4.appspot.com",
    messagingSenderId: "723372497898",
    appId: "1:723372497898:web:0ebb13dcb9ce6d2f6eb093",
    measurementId: "G-J6190VVVQH"
  };
  // Initialize Firebase
  firebase.initializeApp(firebaseConfig);

class Survey extends Component {
    constructor(props) {
        super(props);
        this.state = { 
            uid:uuid.v1(),
            studentName:'',
            answers:{
                answer1:'',
                answer2:'',
                answer3:'',
            },
            isSubmitted:false
         };
    }
    render() {
       var studentName;
       var questions;
         if(this.state.studentName ==='' && this.state.isSubmitted === false){
          <div>
              <h1>Please Enter Your Name:</h1>
             <input type="text" className="form-control" placeholder="Please Enter Your Name"/>
              </div>
         }
        return( 
        <div>
            {studentName}
            ------------------------------
            {questions}
            </div> );}
}

export default Survey;

Answer 1

渲染函数期望您返回 jsx 进行渲染，因此:

 render() {
   if(this.state.studentName ==='' && this.state.isSubmitted === false){
     return (
       <div>
         <h1>Please Enter Your Name:</h1>
         <input type="text" className="form-control" placeholder="Please Enter Your Name"/>
       </div>
    )
   }

   return ( 
     <div>
            {studentName}
            ------------------------------
            {questions}
     </div>
   );
}

另外，修复你的缩进，从长远来看它有助于保持你的理智