Angular Lazy Loading: A Complete Guide

Angular is a popular JavaScript framework for building web applications. It provides a structured approach to web development, offering features such as declarative templates and dependency injection. When looking at the statistics, it can be seen that Angular has 86.7K stars on GitHub . Lazy Load is a technique in Angular that allows you to load modules and components only when they are needed, instead of loading the entire application in advance.

What is angular lazy loading?

Lazy Load is a concept in Angular where modules and components are loaded on demand when the application requires them. Unlike traditional frontloading, which loads all components simultaneously. Lazy Load only loads necessary components when the user navigates to a specific route or performs a specific action.

Lazy Load works by dividing your application into modules. Each module represents a logical section of your application, such as a specific page or a set of related functionality. When the user accesses a route associated with a module, the module and its components are dynamically loaded, thereby reducing initial load time and improving performance.

Benefits of lazy loading

Lazy Load offers several benefits for applications developed by an Angular development company, such as on-demand loading of modules and components, which reduces the initial package size. This leads to better interactivity time and faster rendering, resulting in a smoother user experience. With Lazy Load, Angular development company ensures that only the components and resources required for a specific route or action are loaded, thus optimizing resource utilization and reducing memory overhead.

When to use lazy loading

Lazy loading is particularly useful if your Angular application is large, with multiple modules. Lazy Load can improve initial load time by loading only the necessary modules when navigating to specific routes. It is also useful when your application has a complex routing structure. Lazy loading can simplify Angular module routing configuration and improve overall performance by loading modules on demand.

How to implement lazy loading in Angular

Here is a step-by-step guide on how to implement lazy loading in an Angular application.

Step 1: Configuring Angular Router

Angular Router plays a crucial role in implementing lazy loading. It allows you to define routes to different sections of your application and specify which modules should be lazy loaded. To configure the Angular Router, import the necessary modules into your root module, typically in the app.module.ts file.

import { RouterModule, Routes } from '@angular/router';

Now define your routes using the Routes array.

 const routes: Routes = (
 { path: 'home', component: HomeComponent },
 // Other eagerly loaded routes...
 );

Step 2: Creating a Resource Module

Feature modules are Angular modules that encapsulate a specific feature or section of your application. They are an integral part of lazy loading because you will lazy load them when needed. To create one, generate a new module using the Angular CLI.

 ng generate module feature-module

Then, create the necessary components, services, and other resources in the resource module. After that, export the components, directives, and pipes that will be used outside the resource module by adding them to the exports array in the module's @NgModule decorator.

Step 3: Configuring routes for lazy loading

Now that you're set up, it's time to configure the routes for lazy loading.

In your root module app.module.ts update the route array to include a lazy-loading route.

 const routes: Routes = (
 { path: 'home', component: HomeComponent },
 { path: 'lazy', loadChildren: => import('./feature-module/feature.module').then(m => m.FeatureModule) },
 // Other eagerly loaded routes...
 );

The loadChildren property is used to specify the path to the module and the module class to be lazy loaded. The import function dynamically imports the module. Remove any import statements for the lazy loaded module from the root module as it will now be loaded dynamically.

Step 4: Lazily Loading Resource Modules

To lazy load feature modules in your Angular application, you need to make a small adjustment to the component templates or routing settings that reference the lazy loaded components.

In your template or routing module configuration, update the path to the lazy-loaded component by appending the path defined in the lazy-loaded resource module.

 { path: 'lazy-component', component: LazyComponent }

Switch to

 { path: 'lazy-component', loadChildren: => import('./feature-module/feature.module').then(m => m.LazyComponent) }

This change ensures that the component loads lazy when requested. Be sure to update any other references to lazy-loaded components throughout your application.

And that! You have successfully implemented lazy loading in your Angular application. Now, when a user navigates to a route that requires the lazy-loaded module, it will load on demand, improving your application's initial load time.

Advanced Lazy Loading Strategies

Angular offers advanced strategies for lazy loading, such as preloading modules. Module preloading allows you to load critical modules in the background after the initial page load, improving user experience by reducing subsequent load times.

Preloading strategy in Angular

Preloading is a technique where modules are loaded in the background after the initial page load. Allows the application to load critical modules in advance so that they are immediately available when the user navigates to the corresponding routes.

Preloading provides a balance between performance and user experience. It ensures that essential modules are available when needed, thereby reducing subsequent load times.

Custom preload strategies

Angular allows you to create custom preloading strategies to tune application performance. With a custom preload strategy, you can define which modules to preload and when to load them based on your specific requirements.

By implementing a custom preloading strategy, you have fine-grained control over preloaded modules, thereby optimizing the balance between initial load time and subsequent navigation.

Performance tuning with lazy loading

To measure and improve the performance of an Angular application using lazy loading, consider the following.

Performance metrics and lazy loading

Evaluate key performance metrics such as Time to Interactive (TTI) and First Contentful Paint (FCP). They evaluate the impact of lazy loading on your application's performance. These metrics help you quantify the improvements achieved through lazy loading and identify areas for further optimization.

Optimizing Lazy Loading

Optimize lazy loading using techniques such as bundle size reduction and code splitting. You can also use tools like the webpack package analyzer to analyze and optimize the size of your packages. Make sure your lazy-loading modules are structured efficiently to avoid unnecessary dependencies and code duplication.

Lazy loading with angular libraries

Lazy loading can also be applied to Angular libraries to optimize your application's initial performance.

Understanding Angular Libraries

Angular libraries are packages that contain reusable code such as components, directives, and services. They provide a way to share functionality between multiple Angular applications and improve code maintainability.

How Angular libraries are loaded

By default, Angular libraries are eagerly loaded when the application starts. This means that all library code is bundled with the main application package, leading to an increase in its size and potentially affecting initial load time.

Lazy loading Angular libraries involves dynamically loading library modules when they are needed. This reduces the initial packet size and optimizes the loading process.

Implementing Lazy Loaded Modules for Angular Libraries

Here is a step-by-step guide on how to implement lazy loading for Angular libraries.

Identifying libraries for lazy loading

The first step is to identify which libraries in your Angular application would benefit from lazy loading. Consider libraries that are not frequently used or that are only needed in specific parts of your application.

Creating resource modules for slow libraries

Create a resource module for each library you want to lazy load. For example, if you have a library called ExampleLib. Create a new module called ExampleLibModule using Angular CLI.

ng generate module ExampleLibModule

Within the resource module, import and export the necessary library components, directives, and pipes. This allows other modules to use these components once they are loaded.

Configuring angular router for lazy loading

In your root module, typically app.module.ts, import the Angular Router module:

 import { RouterModule, Routes } from '@angular/router';

Define your routes using the Routes array and configure lazy-loading routes to load resource modules:

 const routes: Routes = (
 { path: 'home', component: HomeComponent },
 { path: 'lazy', loadChildren: => import('./path/to/ExampleLibModule').then(m => m.ExampleLibModule) },
 // Other eagerly loaded routes...
 );

The loadChildren property specifies the path to the resource module and the module class to be lazy loaded.

Updating the application code

Update your application code to use components, directives, and channels from resource modules instead of directly from libraries. For example, if you previously imported an ExampleComponent component from the library like this.

 import { ExampleComponent } from 'example-lib';

Update it to import from the resource module.

 import { ExampleComponent } from './path/to/ExampleLibModule';

Repeat this step for any other places in your application where you use library components, directives, or pipes.

And that! You have successfully implemented lazy loading for Angular libraries. Libraries will now load on demand when associated routes are accessed, improving your application's startup performance.

Testing lazy loading of angular libraries

To test whether lazy loading of Angular libraries is implemented correctly, you can use tools like the Network tab in Chrome DevTools or the webpack Bundle Analyzer.

In the Network tab, observe network requests when navigating different routes in your application. Verify that library modules are loaded on demand and that the module application's initial bundle size is reduced due to lazy loading.

The webpack Bundle Analyzer is a useful tool for viewing and analyzing the size of your bundles. It can provide insights into the impact of lazy loading on your app's package size.

Lazy loading and state management

When it comes to lazy-loading module and state management libraries like NgRx or Akita, there are some considerations to keep in mind for maintaining application state in lazy-loading modules.

Best practices for implementing lazy loading in Angular

Here are some best practices and tips to follow when implementing lazy loading in Angular:

1. Organize your code into feature modules based on the logical sections of your application. This promotes reuse and makes lazy loading easier to manage.
2. Protect your slow routes with appropriate route protectors. Route guards allow you to implement authorization, authentication, and other custom logic before allowing access to a lazy-loaded module.

Conclusion

Lazy Load is a powerful technique in Angular that improves application performance by loading modules and components on demand. With proper implementation and optimization, lazy loading can significantly improve the user experience in your Angular applications. Companies looking to build optimized Angular applications should consider the option of outsourcing Angular development work to a reputable company.

If you liked this article, check out:

• Mastering Angular Routing: A Comprehensive Guide
• Angular Project Structure: Best Practices for Files and Folders
• Dependency Injection in Angular: A Comprehensive Guide
• Mastering Angular Data Binding: A Comprehensive Guide for Experts
• Top Angular UI Component Libraries and Frameworks
• What is Angular and why should your company consider it for development?
• Today's best Javascript frameworks
• Angular for business
• What is the best framework for web development?

common questions

What are the performance implications of using lazy loading in Angular?

The positive performance implications when you load Angular modules slowly is that it leads to faster initial page load, reduced memory usage, and better caching due to only loading the necessary modules on demand. Whereas the negative is that depending on the implementation there may be a slight delay when navigating to a lazy loaded module as it needs to be fetched from the server.

How can I test that lazy loading modules are implemented correctly in my Angular application?

To test whether lazy-loading modules are implemented correctly in your Angular application, you can use network monitoring tools such as Chrome DevTools' Network tab to inspect network requests. Verify that the expected modules are loaded on demand when accessing the corresponding routes.

Can lazy loading be used in combination with other performance optimization techniques in Angular?

Yes, lazy loading can be combined with other performance optimization techniques in Angular such as Code Splliting, Tree Shaking and Preloading.