localStorage is not defined (Angular Universal)

问题:

I am using universal-starter as backbone.

When my client starts, it read a token about user info from localStorage.

@Injectable()
export class UserService {
  foo() {}

  bar() {}

  loadCurrentUser() {
    const token = localStorage.getItem('token');

    // do other things
  };
}

Everything works well, however I got this in the server side (terminal) because of server rendering:

EXCEPTION: ReferenceError: localStorage is not defined

I got the idea from ng-conf-2016-universal-patterns that using Dependency Injection to solve this. But that demo is really old.

Say I have these two files now:

main.broswer.ts

export function ngApp() {
  return bootstrap(App, [
    // ...

    UserService
  ]);
}

main.node.ts

export function ngApp(req, res) {
  const config: ExpressEngineConfig = {
    // ...
    providers: [
      // ...
      UserService
    ]
  };

  res.render('index', config);
}

Right now they use both same UserService. Can someone give some codes to explain how to use different Dependency Injection to solve this?

If there is another better way rather than Dependency Injection, that will be cool too.

---

UPDATE 1 I am using Angular 2 RC4, I tried @Martin's way. But even I import it, it still gives me error in the terminal below:

Terminal (npm start)

/my-project/node_modules/@angular/core/src/di/reflective_provider.js:240 throw new reflective_exceptions_1.NoAnnotationError(typeOrFunc, params); ^ Error: Cannot resolve all parameters for 'UserService'(Http, ?). Make sure that all the parameters are decorated with Inject or have valid type annotations and that 'UserService' is decorated with Injectable.

Terminal (npm run watch)

error TS2304: Cannot find name 'LocalStorage'.

I guess it is somehow duplicated with the LocalStorage from angular2-universal (although I am not using import { LocalStorage } from 'angular2-universal';), but even I tried to change mine to LocalStorage2, still not work.

And in the meanwhile, my IDE WebStorm also shows red:

BTW, I found a import { LocalStorage } from 'angular2-universal';, but not sure how to use that.

---

UPDATE 2, I changed to (not sure whether there is a better way):

import { Injectable, Inject } from '@angular/core';
import { Http } from '@angular/http';
import { LocalStorage } from '../../local-storage';

@Injectable()
export class UserService {
  constructor (
    private _http: Http,
    @Inject(LocalStorage) private localStorage) {}  // <- this line is new

  loadCurrentUser() {
    const token = this.localStorage.getItem('token'); // here I change from `localStorage` to `this.localStorage`

    // …
  };
}

This solves the issue in UPADAT 1, but now I got error in the terminal:

EXCEPTION: TypeError: this.localStorage.getItem is not a function

回答1:

Update for newer versions of Angular

OpaqueToken was superseded by InjectionToken which works much in the same way -- except it has a generic interface InjectionToken<T> which makes for better type checking and inference.

Orginal Answer

Two things:

1. You are not injecting any object that contains the localStorage object, you are trying to access it directly as a global. Any global access should be the first clue that something is wrong.
2. There is no window.localStorage in nodejs.

What you need to do is inject an adapter for localStorage that will work for both the browser and NodeJS. This will also give you testable code.

in local-storage.ts:

import { OpaqueToken } from '@angular/core';

export const LocalStorage = new OpaqueToken('localStorage');

In your main.browser.ts we will inject the actual localStorage object from your browser:

import {LocalStorage} from './local-storage.ts';

export function ngApp() {
  return bootstrap(App, [
    // ...

    UserService,
    { provide: LocalStorage, useValue: window.localStorage}
  ]);

And then in main.node.ts we will use an empty object:

... 
providers: [
    // ...
    UserService,
    {provide: LocalStorage, useValue: {getItem() {} }}
]
...

Then your service injects this:

import { LocalStorage } from '../local-storage';

export class UserService {

    constructor(@Inject(LocalStorage) private localStorage: LocalStorage) {}

    loadCurrentUser() {

        const token = this.localStorage.getItem('token');
        ...
    };
}

回答2:

In Angular 4 (and 5) you can easily deal with such issue with a simple function in the following way:

app.module.ts

@NgModule({
    providers: [
        { provide: 'LOCALSTORAGE', useFactory: getLocalStorage }
    ]
})
export class AppModule {
}

export function getLocalStorage() {
    return (typeof window !== "undefined") ? window.localStorage : null;
}

If you have a server/client split file AppModule, place it in the app.module.shared.ts file - the function won't break your code - unless you need to enforce completely different behaviours for the server and client builds; if that’s the case, it could be wiser to implement a custom class factory instead, just like it has been shown in other answers.

Anyway, once you're done with the provider implementation, you can inject the LOCALSTORAGE generic in any Angular component and check for the platform type with the Angular-native isPlatformBrowser function before using it:

import { PLATFORM_ID } from '@angular/core';
import { isPlatformBrowser, isPlatformServer } from '@angular/common';

@Injectable()
export class SomeComponent {
    constructor(
        @Inject(PLATFORM_ID) private platformId: any,
        @Inject('LOCALSTORAGE') private localStorage: any) {

        // do something

    }

    NgOnInit() {
        if (isPlatformBrowser(this.platformId)) {
            // localStorage will be available: we can use it.
        }
        if (isPlatformServer(this.platformId)) {
            // localStorage will be null.
        }
    }
}

It’s worth noting that, since the getLocalStorage() function will return null if the window object isn’t available, you could just check for this.localStorage nullability and entirely skip the platform type check. However, I strongly recommend the above approach as that function implementation (and return value) might be subject to change in the future; conversely, the isPlatformBrowser / isPlatformServer return values are something that can be trusted by design.

For more info, check out this blog post that I wrote on the topic.

回答3:

I don't think this is a good solution, but I was stucked with the same problem using aspnetcore-spa generator and solved it this way:

@Injectable()
export class UserService {
  foo() {}

  bar() {}

  loadCurrentUser() {
    if (typeof window !== 'undefined') {
       const token = localStorage.getItem('token');
    }

    // do other things
  };
}

This condition prevents client code from running on the server-side where 'window' object doesn't exist.

回答4:

I am having a similar issue with Angular 4 + Universal following steps here to configure a SPA that can render at client side or server side.

I am using oidc-client because I need my SPA to act as an OpenId Connect/Oauth2 client for my Identity Server.

The thing is that I was having the typical problem where localStorage or sessionStorage are not defined in server side (they only exist when there's a window object, therefore it wouldn't make sense for nodeJs to have these objects).

I have unsuccessfully tried the approach to mock the localStorage or sessionStorage and use the real one when in browser and an empty one in server.

But I came to the conclusion that for my needs I don't really need localStorage or sessionStorage to do anything in server side. If executed in NodeJs, simply skip the part where sessionStorage or localStorage is used, and the execution will then happen at client-side.

This would suffice:

console.log('Window is: ' + typeof window);
    this.userManager = typeof window !== 'undefined'? new oidc.UserManager(config) : null; //just don't do anything unless there is a window object

In client-side rendering it prints: Window is: object

In nodeJs it prints: Window is: undefined

The beauty of this is that Angular Universal will simply ignore the execution/rendering at server side when there is no window object, BUT that execution will be working fine when Angular Universal sends the page with javascript to the browser, therefore even if I am running my app in NodeJs eventually my browser prints the following: Window is: object

I know this is not a proper answer for those who really need to access localStorage or sessionStorage in server side, but for most of the cases we use Angular Universal simply to render whatever is possible to render in server side, and for sending the things that can't be rendered to the browser to work normally.

回答5:

Thanks for @Martin's great help. But there are several places below need to be updated to get it work:

• constructor in user.service.ts
• useValue in main.node.ts, main.browser.ts

This is how my codes look like now.

I would love to accept @Martin's answer when he updated.

BTW, I found a import { LocalStorage } from 'angular2-universal';, but not sure how to use that.

user.service.ts

import { Injectable, Inject } from '@angular/core';

import { LocalStorage } from '../local-storage';

@Injectable()
export class UserService {
  constructor (
    @Inject(LocalStorage) private localStorage) {}

  loadCurrentUser() {
    const token = localStorage.getItem('token');

    // do other things
  };
}

local-storage.ts

import { OpaqueToken } from '@angular/core';

export const LocalStorage = new OpaqueToken('localStorage');

main.broswer.ts

import { LocalStorage } from './local-storage';

export function ngApp() {
  return bootstrap(App, [
    // ...

    { provide: LocalStorage, useValue: window.localStorage},
    UserService
  ]);
}

main.node.ts

import { LocalStorage } from './local-storage';

export function ngApp(req, res) {
  const config: ExpressEngineConfig = {
    // ...
    providers: [
      // ...

      { provide: LocalStorage, useValue: { getItem() {} }},
      UserService
    ]
  };

  res.render('index', config);
}

回答6:

This is how we have it in our project, as per from this github comment:

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

export class SomeClass implements OnInit {

    constructor(@Inject(PLATFORM_ID) private platformId: Object) { }

    ngOnInit() {
        if (isPlatformServer(this.platformId)) {
            // do server side stuff
        }

        if (isPlatformBrowser(this.platformId)) {
           localStorage.setItem('myCats', 'Lissie & Lucky')
        }
    }    
}

回答7:

I have no sufficient knowledge of preparing angular apps to run serverside. But in the similar scenario for react & nodejs, what needs to be done is to let server know what localStorage is. For example:

//Stub for localStorage
(global as any).localStorage = {
  getItem: function (key) {
    return this[key];
  },
  setItem: function (key, value) {
    this[key] = value;
  }
};

Hope this can be of any help to you.

回答8:

As stupid as this approach might seem, it is working, and I had to do none of the plumbing the other answers are suggesting.

Step 1

Install localstorage-polyfill: https://github.com/capaj/localstorage-polyfill

Step 2

Assuming you followed this step: https://github.com/angular/angular-cli/wiki/stories-universal-rendering, you should have a file called, server.js in your project root folder.

In this server.js add this:

import 'localstorage-polyfill'

global['localStorage'] = localStorage;

Step 3

Rebuild your project, npm run build:ssr, and all should work fine now.

---

Does the above approach work? Yes, as far as I can tell.

Is it the best? Maybe not

Any performance issues? Not that I know of. Enlighten me.

However, as it stands now, this is the dumbest, most cleanest approach to getting my localStorage to pass

回答9:

I have also ran in to the same issue. You can write inside 'isBrowser' check by importing below statement.

import { isBrowser } from 'angular2-universal';