使用 Angular Universal 的服务器端渲染 (SSR)

Question

为了创建服务器端应用程序模块，我使用了这个命令

ng add @nguniversal/express-engine

然后，我运行了命令： npm run build:ssr ，构建成功。

之后我跑了 npm run serve:ssr，但出现以下错误

*****************-u:~/practice-angular$ npm run serve:ssr

> practice-angular@0.0.0 serve:ssr /home/bhavya/practice-angular
> node dist/practice-angular/server/main.js

/home/bhavya/practice-angular/dist/practice-angular/server/main.js:364478
        redirectTo: localStorage.getItem('countryCode') || 'my'
                    ^

ReferenceError: localStorage is not defined
    at Object../src/app/app-routing.module.ts (/home/bhavya/practice-angular/dist/practice-angular/server/main.js:364478:21)
    at __webpack_require__ (/home/bhavya/practice-angular/dist/practice-angular/server/main.js:20:30)
    at Object../src/app/app.module.ts (/home/bhavya/practice-angular/dist/practice-angular/server/main.js:364599:30)
    at __webpack_require__ (/home/bhavya/practice-angular/dist/practice-angular/server/main.js:20:30)
    at Object../src/app/app.server.module.ts (/home/bhavya/practice-angular/dist/practice-angular/server/main.js:364718:22)
    at __webpack_require__ (/home/bhavya/practice-angular/dist/practice-angular/server/main.js:20:30)
    at Object../src/main.server.ts (/home/bhavya/practice-angular/dist/practice-angular/server/main.js:388159:27)
    at __webpack_require__ (/home/bhavya/practice-angular/dist/practice-angular/server/main.js:20:30)
    at Object../server.ts (/home/bhavya/practice-angular/dist/practice-angular/server/main.js:364353:23)
    at __webpack_require__ (/home/bhavya/practice-angular/dist/practice-angular/server/main.js:20:30)
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! practice-angular@0.0.0 serve:ssr: `node dist/practice-angular/server/main.js`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the practice-angular@0.0.0 serve:ssr script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /home/bhavya/.npm/_logs/2021-09-03T08_32_02_929Z-debug.log

为了解决这个错误，我按照answer 中提到的步骤进行操作。但是，我仍然无法解决这个问题。谁能帮我解决这个问题？

Answer 1

当您的代码在服务器端执行时，您在浏览器中拥有的一些 API，如 localStorage 和 sessionStorage 不可用。一个解决方案是注入 PLATFORM_ID 并使用 isPlatformBrowser 函数来访问此 API，前提是您仅在浏览器环境中。

import { Component, OnInit, Inject } from '@angular/core';
import { PLATFORM_ID } from '@angular/core';
import { isPlatformBrowser} from '@angular/common';

@Component({
  selector: 'your-component',
  templateUrl: 'your-component.component.html',
  styleUrls: ['your-component.component.css'],
})
export class YourComponent implements OnInit { 
  constructor(@Inject(PLATFORM_ID) private _platformId: Object) {}

  ngOnInit() {  
    if (isPlatformBrowser(this._platformId)) {
      // here you can access localStorage
    } else {
      // here you are on the server side and localStorage is not available
    }
  }
}

有一种方法可以在服务器端获取 localStorage，例如使用node-localstorage，但是您将在服务器上拥有一个localStorage，在浏览器中拥有一个，如果您想共享数据，您必须找到同步它们的方法。