Lazy loading of routes causing flickering issue

Lazy loading in Angular, React, Vue, or other frameworks is a great way to improve performance by loading modules or components only when needed. However, it can cause a flickering issue where a blank screen or default state appears briefly before the content loads. Below, I’ll explain why this happens and how to fix it.

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1. Why Does the Flickering Issue Occur?

The flickering issue in lazy loading usually happens due to:

1. No Proper Loading Indicator
   • When a route is being lazily loaded, there is a delay before the component appears, causing a blank screen.
2. Route Module Not Preloaded
   • If lazy-loaded modules take longer to load, the transition may appear jarring.
3. CSS or Styling Issues
   • A delay in applying styles can result in a quick flash of unstyled content.
4. Multiple Renders in React (Strict Mode)
   • In React, React.StrictMode may cause components to mount and unmount multiple times in development.
5. Slow Network or API Calls
   • If the page depends on API data, it might show a blank UI before the content is fetched.

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2. How to Fix Flickering Issues in Lazy Loaded Routes?

Solution 1: Use a Loading Indicator (Skeleton or Spinner)

A simple loading spinner or skeleton screen can prevent the flickering effect by showing a placeholder while the content is loading.

Angular Example

Modify app-routing.module.ts:

const routes: Routes = [
  { 
    path: 'dashboard', 
    loadChildren: () => import('./dashboard/dashboard.module').then(m => m.DashboardModule),
    data: { preload: true } 
  }
];

Then, in the parent component:

<ng-container *ngIf="isLoading; else loadedContent">
  <app-spinner></app-spinner>  <!-- Show spinner while loading -->
</ng-container>
<ng-template #loadedContent>
  <router-outlet></router-outlet>
</ng-template>

React Example

const LazyComponent = React.lazy(() => import("./Dashboard"));

function App() {
  return (
    <Suspense fallback={<div>Loading...</div>}>
      <LazyComponent />
    </Suspense>
  );
}

Why This Works?
The fallback component shows until the module is loaded, preventing flickering.

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Solution 2: Preloading Lazy-Loaded Modules

To avoid delays in loading, you can preload lazy-loaded modules in Angular.

Angular Preloading Strategy

Modify app-routing.module.ts:

import { PreloadAllModules } from '@angular/router';

const routes: Routes = [
  { 
    path: 'dashboard', 
    loadChildren: () => import('./dashboard/dashboard.module').then(m => m.DashboardModule) 
  }
];

@NgModule({
  imports: [RouterModule.forRoot(routes, { preloadingStrategy: PreloadAllModules })],
  exports: [RouterModule]
})
export class AppRoutingModule { }

Why This Works?

• Modules will load in the background, reducing flickering when the user navigates.

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Solution 3: Optimize CSS and Avoid Flash of Unstyled Content (FOUC)

Sometimes, styles are loaded after the component, causing a brief flicker.
Fix: Ensure styles are preloaded or use CSS inlining.

Example:

<link rel="stylesheet" href="styles.css" as="style" onload="this.rel='stylesheet'">

Why This Works?

• It ensures styles are applied before the page loads, preventing the flicker.

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Solution 4: Prevent Multiple Mounting in React

In React, React.StrictMode in development causes double rendering. You can disable it in index.js:

<React.StrictMode>
  <App />
</React.StrictMode>

Remove StrictMode in production builds if it causes flickering.

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Solution 5: Use Route-Level Caching to Avoid Reloading

If the issue occurs every time the user navigates, caching previously loaded components helps.

Angular Example: Route Reuse Strategy

Modify app-routing.module.ts:

import { RouteReuseStrategy } from '@angular/router';

@NgModule({
  providers: [{ provide: RouteReuseStrategy, useClass: CustomReuseStrategy }]
})
export class AppModule { }

Then, create CustomReuseStrategy.ts:

export class CustomReuseStrategy implements RouteReuseStrategy {
  shouldDetach(): boolean { return true; }
  store(): void {}
  shouldAttach(): boolean { return true; }
  retrieve(): any { return null; }
  shouldReuseRoute(): boolean { return true; }
}

Why This Works?
It caches routes, preventing flickering when switching back to a lazy-loaded module.