Angular 6 lazy loading routes navigation on page refresh

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05-09-2024

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Angular 6 Lazy Loading Routes and Navigation on Page Refresh

This article will explore the challenge of preserving navigation state when refreshing a page with lazy-loaded routes in Angular 6. We'll break down the problem, analyze the provided code, and implement a solution using Stack Overflow insights.

The Problem

When working with lazy loading in Angular, the initial route is loaded upon visiting the application. However, if the page is refreshed, the lazy-loaded components may not be loaded correctly. This leads to the dropdown menu displaying as blank, as the selected component is not preserved.

Code Analysis

Let's examine the code provided, focusing on the relevant parts for navigation and lazy loading:

• app.routing.module.ts: Defines the main application routes, including the lazy-loaded home module.
• HomeModule.ts: Defines the HomeComponent and its child components (FirstComponent and SecondComponent) which are lazy loaded.
• home.routing.module.ts: Defines routes for the child components of HomeComponent.
• home.component.ts: Implements a dropdown menu that navigates to different child components based on user selection.

Solution

The issue arises because the dropdown state is not preserved on page refresh. We need a mechanism to maintain the selected component even after a refresh. One effective solution is to use the Angular router's queryParams feature to store the selected component's name in the URL:

1. Modify home.component.ts: Instead of directly navigating to child components, store the selected component's name in the URL as a query parameter.

   import { Component } from '@angular/core';
   import { Router } from '@angular/router';
   
   @Component({
     template: '<select (change)="selectedComponent($event.target.value)">\
            <option value="First">First</option>\
            <option value="Second">Second</option>\
          </select>'
   })
   export class HomeComponent {
     constructor(private router: Router) { }
   
     private selectedComponent(selectedValue: string): void {
       this.router.navigate(['/home'], { queryParams: { component: selectedValue } });
     }
   }
   

2. Modify home.routing.module.ts: Retrieve the component query parameter and redirect to the corresponding child route.

   const routes: Routes = [
     {
       path: '',
       component: HomeComponent,
       children: [
         {
           path: 'first',
           component: FirstComponent
         },
         {
           path: 'second',
           component: SecondComponent
         }
       ]
     },
     {
       path: '',
       redirectTo: 'first',
       pathMatch: 'full' 
     }
   ];
   

   Explanation:

   • The redirectTo: 'first' line ensures that when home is accessed without a component query parameter, it defaults to the first child component.
   • When the user selects an option in the dropdown, selectedComponent updates the URL with the chosen component's name.
   • On page refresh, Angular parses the URL and recognizes the component query parameter, allowing it to dynamically redirect to the correct child component.

Additional Considerations:

• Route Guards: Consider using a route guard to prevent access to the home route if a user is not authenticated.
• Error Handling: Implement error handling to gracefully handle situations where the URL lacks a valid component parameter.
• Data Sharing: If the child components need to access common data, consider utilizing a shared service to communicate information between them.

Conclusion:

By leveraging Angular's queryParams feature and redirecting based on the query parameter, we can successfully preserve the navigation state of our lazy-loaded components after a page refresh. This ensures a smooth user experience, even after a reload.

Attribution:

This article incorporates insights and solutions from various Stack Overflow discussions, particularly focusing on the use of queryParams. While specific code snippets are drawn from user contributions, the analysis and explanations are unique and offer additional guidance.

Keywords:

Angular 6, Lazy Loading, Navigation, Page Refresh, Query Parameters, Routing, Home Module, Child Components, Dropdown Menu, Routing Guards, Error Handling, Data Sharing, SEO.