Javascript - How to detect Browser Refresh using Angular

Javascript - How to detect Browser Refresh using Angular

Detecting a browser refresh in an Angular application can be achieved by listening to window events and differentiating between a page reload and other forms of navigation like using the Angular router. However, Angular itself doesn't provide a direct way to distinguish a page reload from other navigations, so we typically rely on native JavaScript events and properties.

Here's a common approach using the window.performance object and the NavigationStart event from Angular's router:

  1. Inject the Router: First, you need to inject Angular's Router into your component or service.

  2. Use NavigationStart Event: Listen to the NavigationStart event from the Router. This event is fired when navigation starts.

  3. Check performance.navigation or performance.getEntriesByType("navigation"): Inside the event listener, you can use the window.performance object to check if the navigation is a result of a page reload.

Here's an example of how you might implement this:

import { Component, OnInit } from '@angular/core'; import { Router, NavigationStart } from '@angular/router'; @Component({ // component metadata }) export class AppComponent implements OnInit { constructor(private router: Router) {} ngOnInit() { this.router.events.subscribe(event => { if (event instanceof NavigationStart) { const nav = window.performance.getEntriesByType("navigation")[0]; if (nav.type === 'reload') { console.log('This is a page refresh'); } else { console.log('This is not a page refresh'); } } }); } }

Explanation:

  • window.performance.getEntriesByType("navigation"): This gets an array of PerformanceNavigationTiming objects, which contain information about the type of navigation event. If it's a refresh, nav.type will be 'reload'.

  • NavigationStart: This is an Angular router event that gets triggered when navigation starts.

Points to Note:

  • The performance API and its properties are well-supported in modern browsers, but you should still check for browser compatibility if your application targets older browsers.
  • This method relies on checking the type of navigation event right after it starts. It's a generally reliable method, but keep in mind that it's more of a workaround than a built-in Angular feature for detecting page reloads.
  • If you need to handle a page refresh in a specific way (like preserving state or prompting the user), it's good practice to handle this in a service rather than directly in a component for better separation of concerns and reusability.

  1. Using HostListener in Angular Component:

    import { Component, HostListener } from '@angular/core'; @Component({ selector: 'app-example', template: '<p>Angular Component</p>', }) export class ExampleComponent { @HostListener('window:beforeunload', ['$event']) unloadHandler(event: Event): void { // Handle refresh or unload event console.log('Page is being refreshed'); } }

    Description: This approach uses the HostListener decorator to listen for the beforeunload event on the window.

  2. Using Router Navigation Events:

    import { Component, OnInit } from '@angular/core'; import { Router, NavigationStart } from '@angular/router'; @Component({ selector: 'app-example', template: '<p>Angular Component</p>', }) export class ExampleComponent implements OnInit { constructor(private router: Router) { } ngOnInit(): void { this.router.events.subscribe(event => { if (event instanceof NavigationStart) { // Check if navigation is a page refresh if (event.navigationTrigger === 'imperative') { console.log('Page is being refreshed'); } } }); } }

    Description: This method uses Angular Router's navigation events to detect when the page is being refreshed.

  3. Using NgZone and Platform:

    import { Component, NgZone, PLATFORM_ID, Inject } from '@angular/core'; import { isPlatformBrowser } from '@angular/common'; @Component({ selector: 'app-example', template: '<p>Angular Component</p>', }) export class ExampleComponent { constructor( private ngZone: NgZone, @Inject(PLATFORM_ID) private platformId: Object ) { if (isPlatformBrowser(this.platformId)) { this.ngZone.runOutsideAngular(() => { window.addEventListener('beforeunload', () => { console.log('Page is being refreshed'); }); }); } } }

    Description: This approach uses NgZone to run the event listener outside Angular's zone to avoid change detection issues.

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