javascript - react 类型错误: Cannot read property 'replace' of undefined

Question

我不明白为什么我的组件的渲染函数中的替换函数出现错误。

类型错误:无法读取未定义的属性“替换”

我只是尝试替换 services.serviceImage 中的字符串值，并替换像 "react-site/public/","" 这样的字符串，就像通常对任何字符串所做的那样，我做了一些测试，我可以确认返回的值是一个字符串，我做了一些其他字符串替换，它起作用了，但在这种情况下有些东西不起作用......为什么？

我已经尝试过作为正则表达式方法，但没有成功:

imgUrl = imgUrl.replace("/react\-site\/public/g", "");

由于某种原因，我的 Node 服务器也不接受 doc.serviceImage 响应的替换方法!!!

我在这里做错了什么......？

我的完整代码:

import React, {Component} from 'react';
import axios from 'axios';
//import { Link } from "react-router-dom";
import './catalogue.scss';

class ServicesPage extends Component {
  state = {
    services: [],
    loading: false
  }
  componentDidMount(){

    this.setState({
      loading: true
    });

    axios.get('/services')
    .then(response => {
      console.log(response);
      this.setState({
        services: response.data.services,
        loading: false
      });
    })
    .catch( error => {
      console.log(error);
    });
    document.title = "Pain Relief and Massage Services - LA Therapy";
  }//componentDidMount

  replaceStr(str, newStr) {
   return  str = str.replace(str, newStr);
  }

  render(){

    let pageRender; 
    if(this.state.loading){
     pageRender =  <div className="pageLoader">Loading... <img src="./images/ui/spinner.svg"/></div>
    }else{
      {this.state.services.map(services => {
        let backgroundUrl = {};
        let imgUrl = services.serviceImage;

        imgUrl = imgUrl.replace("/react\-site\/public/g", ""); //this string replace is not working

        console.log(imgUrl);


        if (services.serviceImage) {

           backgroundUrl = {
            backgroundImage: `url(${imgUrl})`,
            backgroundSize: 'cover'  
          };

        }else{
         backgroundUrl = {
            backgroundImage: 'url(./images/ui/add-image-wide.png)',
            backgroundSize: 'cover'  
          };

          pageRender =  <div className="columns white-bg">
          <div className="grid-x">
          {this.state.services.map(services =>

            <div key={services._id} className="cell large-6 medium-12 small-12 end padding-all-3x">
            <div className="catalogue-medium gray_2-border white-bg margin-distributed round-small" style={backgroundUrl}>
              <div className="dark-overlay"></div>
              <img src="./uploads/services/1538735070981-1538653957308-back-massage.jpg"/>
              <div className="tittle-bottom">{services.name} </div>
            </div>
            </div> 
            )}
          </div>
        </div>


        }

        })
      }
    }

    return(
      <div>
        {pageRender}
      </div>
    );
  }
}

export default ServicesPage;

Answer 1

您在使用后查看该属性是否有效

let imgUrl = services.serviceImage;  <-- read it
imgUrl = imgUrl.replace(...)  <-- where the error occurs
if (services.serviceImage) {  <-- is truthy

因此将逻辑移至检查内部

let imgUrl = services.serviceImage; 
if (services.serviceImage) {  
  imgUrl = imgUrl.replace(...)

或者如果您出于某种原因需要 if 之外的 imgUrl 将其设置为空字符串

let imgUrl = services.serviceImage || '';
imgUrl = imgUrl.replace(...)