Angular 17 window not defined

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04-10-2024

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Angular 17: "Window is not defined" - A Common Error and How to Fix It

Angular applications, like any JavaScript-based application, often rely on the browser's built-in window object to access various browser-specific features. This object provides access to things like the DOM (Document Object Model), browser history, local storage, and more.

However, a common error encountered in Angular 17 development is the infamous "window is not defined" error. This occurs when trying to access window within a context where it doesn't exist, typically during server-side rendering (SSR) or within a unit test environment. Let's understand why this happens and explore the solutions.

Understanding the "window is not defined" Error

The window object is specific to the browser environment. When Angular runs on the server during SSR, there's no browser window available, hence the error. Similarly, during unit tests, the testing environment doesn't necessarily mimic the full browser environment. This lack of a browser context leads to the window object being undefined.

Scenarios and Solutions

Let's examine common scenarios where this error arises and the solutions:

1. Accessing window in a Service:

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

@Injectable({
  providedIn: 'root'
})
export class MyService {
  getLocation() {
    return window.location.href; // Error: window is not defined
  }
}

Solution: Use platform-browser's isPlatformBrowser function to conditionally access window only in the browser environment:

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

@Injectable({
  providedIn: 'root'
})
export class MyService {
  constructor(@Inject(PLATFORM_ID) private platformId: object) {}

  getLocation() {
    if (isPlatformBrowser(this.platformId)) {
      return window.location.href; 
    }
    return null; // Or handle the case where the window is not available
  }
}

2. Accessing window in a Component:

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

@Component({
  selector: 'app-my-component',
  template: `
    <p>Current URL: {{getLocation()}}</p> 
  `
})
export class MyComponent {
  getLocation() {
    return window.location.href; // Error: window is not defined
  }
}

Solution: You can use the same approach as in the service example, checking isPlatformBrowser in the component's constructor.

3. window in Unit Tests:

import { MyComponent } from './my.component';

describe('MyComponent', () => {
  let component: MyComponent;

  beforeEach(() => {
    component = new MyComponent(); // Assuming no dependencies 
  });

  it('should get the current URL', () => {
    expect(component.getLocation()).toBe(window.location.href); // Error: window is not defined
  });
});

Solution: Use a mocking library like jest to create a mock window object for your tests:

import { MyComponent } from './my.component';

describe('MyComponent', () => {
  let component: MyComponent;
  const mockWindow = { location: { href: 'http://example.com' } };

  beforeEach(() => {
    component = new MyComponent();
    Object.defineProperty(global, 'window', { value: mockWindow, writable: true });
  });

  it('should get the current URL', () => {
    expect(component.getLocation()).toBe('http://example.com'); 
  });

  afterEach(() => {
    delete (global as any).window; 
  });
});

Best Practices

• Avoid direct window access: Whenever possible, use Angular's built-in services like Location for navigation, DomSanitizer for DOM manipulation, and other appropriate services to avoid direct window access.
• Use isPlatformBrowser: This is the recommended way to check if you're running in the browser environment, and therefore safely use window.
• Consider your context: Remember that certain functionality might be specific to the browser environment, and it's crucial to design your application accordingly.

Conclusion

The "window is not defined" error is a common problem in Angular development, especially when dealing with SSR or unit tests. By understanding the underlying reasons and implementing appropriate solutions, you can effectively avoid this error and ensure your Angular applications work seamlessly across various environments.