React - “localStorage is not defined” error showing

问题

I am trying to make my website SEO friendly with meta tags. I am implementing server-side rendering in my application. After this, I am getting the following error:

ReferenceError: localStorage is not defined.

Please help how to resolve it.

My package.json:

{


 "main": "server.js",
 "scripts": {
  "start-dev": "NODE_ENV=development webpack -w & NODE_ENV=development node server.js",
  "test": "echo \"Error: no test specified\" && exit 1"
 },
 "keywords": [],
 "author": "",
 "license": "ISC",
 "dependencies": {
  "axios": "^0.18.0",
  "express": "^4.15.3",
  "firebase": "^4.12.1",
  "html2canvas": "^1.0.0-alpha.12",
  "react": "^16.2.0",
  "react-adsense": "0.0.5",
  "react-dom": "^16.2.0",
  "react-facebook-login": "^4.0.1",
  "react-google-login": "^3.2.1",
  "react-meta-tags": "^0.3.0",
  "react-router-dom": "^4.2.2",
  "react-router-match-as-promised": "^1.0.5",
  "react-scripts": "1.1.1",
  "react-share": "^2.1.1",
  "react-slick": "^0.22.3"
 },
 "devDependencies": {
  "autoprefixer": "^7.1.2",
  "babel-core": "^6.25.0",
  "babel-loader": "^7.1.1",
  "babel-preset-es2015": "^6.24.1",
  "babel-preset-react-app": "^3.1.2",
  "babel-preset-stage-0": "^6.24.1",
  "css-loader": "^0.28.4",
  "extract-text-webpack-plugin": "^2.1.2",
  "file-loader": "^0.11.2",
  "postcss-loader": "^2.0.6",
  "webpack": "^3.1.0",
  "webpack-node-externals": "^1.7.2"
 }
}

Meta Tags commonly used in all pages. Home.js

<code>
import React, { Component } from 'react';
import axinst from '../common';
import {TabBox,TabBox2,TabBox3} from '../common/tabbox';
import Ads  from '../common/ads';
import SubscribeFrm from '../common/subscribefrm';
import MetaTags from 'react-meta-tags';
import AdSense from 'react-adsense';
import Loader from '../common/loader';

class Home extends Component {
  constructor(props) {
    super(props);
  }

  state = {
    header:[],
    otherSports:[],
    wizztalk:[],
    sports:[],
    isProgress:'',
    activeCat: '',
    metaTitle:'',
    metaDesc:'',
    metaKey:''
  }

  componentDidMount(){


    // axinst.get('/home')
    this.setState({isProgress:true});
    axinst.get('/home').then(response => {
      this.setState({isProgress:false});
      const header = response.data.data.Header;
      const sports = response.data.data.Sports;
      const otherSports = response.data.data.OtherSports;
      const wizztalk = response.data.data.Wizztalk;
      const metaTitle = response.data.data.metaTitle;
      const metaDesc = response.data.data.metaDesc;
      const metaKey = response.data.data.metaKeyword;
      this.setState({header});
      this.setState({sports});
      this.setState({otherSports})
      this.setState({wizztalk});
      this.setState({metaTitle});
      this.setState({metaDesc});
      this.setState({metaKey});
    }).catch(function (error) {
      // console.log(error);
      // console.log('error');
    });
  }

  render() {
    const hD = this.state.header;
    const sport = this.state.sports;
    return (
    <div id="maincontent">
        <MetaTags>
          <title>{this.state.metaTitle}</title>
          <meta name="title" content={this.state.metaTitle} />
          <meta name="keywords" content={this.state.metaKeyword} />
          <meta name="description" content={this.state.metaDesc} />
          <meta name="og:description" content={this.state.metaDesc} />
          <meta name="og:title" content={this.state.metaTitle} />
          <meta name="og:image" content={process.env.PUBLIC_URL +"/images/logo.png"}/>
        </MetaTags>
</code>

回答1:

When you're rendering on the server, you do not have a browser and thus you do not have access to all the APIs that the browser provides, including localStorage.

In JavaScript code that is running both on the server and on the client (browser), it is common practice to guard against with an if clause that checks if window is defined. “Window” is the root object provided by the browser for all the APIs that are provided by the browser.

Example:

if (typeof window !== 'undefined') {
    console.log('we are running on the client')
} else {
    console.log('we are running on the server');
}

In your case, you want to put your call to localStorage in such an if clause, for example:

if (typeof window !== 'undefined') {
    localStorage.setItem('myCat', 'Tom');
}

回答2:

You can add a polyfill to your app. I.e. somewhere in your index.js:

if (!window) {
    require('localstorage-polyfill');
}

来源：https://stackoverflow.com/questions/52474208/react-localstorage-is-not-defined-error-showing