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Last Updated: Mar 27, 2024

Angular Lazy Loading

Author Vidhi Sareen
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Just imagine, you have to create a presentation on a topic and the deadline is on your head. While you search for information on the internet, suddenly a big sign showing “LOADING” appears. It's irritating right?. Let's take an example like you are really hungry and when you order the food then suddenly the site hangs.

Angular Lazy Loading

It will surely make you really angry.  It creates a negative first impression on the user and leads to changing of the site or abandoning the site. To solve this problem, we can use lazy loading. In this article, we are going to discuss what is Angular lazy loading, what are some important features of lazy loading and in what scenarios we can use lazy loading and many more.

Lazy Loading

Lazy loading is a technique in which loading resources like videos or images, or photos is involved. It does not involve all the resources at once. They are displayed when they are required. It reduces the starting loading time when the user opens the website or an app. It is highly beneficial when there is a low network available. We can view the entire website using the scroll-down option. However, we can use lazy loading to improve the speed of the website. It may require some techniques and specifications while implementing it.

Steps to Implement Angular Lazy Loading 

These are the steps that one should follow in order to implement Angular Lazy Loading.

Create a New Angular Project for Implementing Lazy Loading

ng new angular-lazy-loading

Using the command ‘ng new angular-lazy-loading’ is used to create a fresh new project.  

Create a New Module Using CLI Command

ng new coding_ninja-app --routing

It will create a new module to hold all the components of lazy-loading and add it to the app module as a child module.

Create Components in a New Module Using the CLI Command

ng generate module course --route course --module app.module
ng generate module Test --route Test --module app.module

It will create new components in a new module. Here we have created two components named as course and test.

const routes: Routes = [{ path: 'coding_ninja', loadChildren: () => import('./coding-ninja/coding-ninja.module').then(m => m.CodingNinjaModule) }, 
{ path: 'course', loadChildren: () => import('./course/course.module').then(m => m.CourseModule) },
 { path: 'Test', loadChildren: () => import('./test/test.module').then(m => m.TestModule) }];

The lazy loading syntax uses loadChildren() function that uses ‘import’ function in the syntax for dynamically importing the modules. The path indicates the reference path to the module.

There are two ways in which it can be implemented:

Using Promise

{path: 'lazy-loading',
     loadChildren: () => import('./lazy-loading/lazy-loading.module')
       .then(m => m.LazyLoadingModule)
            .catch(err => {
                  console.log('Error loading lazy module:', err);
            return null;

You can use promises to handle the Loading of the components or resources. A promise constructor is used to create a promise and resolve it when it is done with loading the resources.

Using Async

{path: 'lazy-loading',
   async () => (await import('./lazy-loading/lazy-loading.module’)).LazyLoadingModule
       .then(m => m.LazyLoadingModule)
                      .catch(err => {
                               console.log('Error loading lazy module:', err);
                      return null;

Using async will help you to create readable and presentable code. This 'await' keyword is used, pausing the function execution until the Promise returned by ''import'' is resolved.

Set User Interface

To display the information of the application we have created a simple UI. We have included the title and two options like course and test for access to the information regarding the course and test offered by the application.


<button type="button" routerLink="/course">course</button>
<button type="button" routerLink="/Test">Test</button>

Import and Route the Configure

Added a default path to match those who do not belong to the other two paths.

const routes: Routes = [{ path: 'coding_ninja', loadChildren: () => import('./coding-ninja/coding-ninja.module').then(m => m.CodingNinjaModule) }, 
{ path: 'course', loadChildren: () => import('./course/course.module').then(m => m.CourseModule) },
 { path: 'Test', loadChildren: () => import('./test/test.module').then(m => m.TestModule)},
 { path: '', redirectTo: '', pathMatch: 'full } ];

Test and verify that Lazy Loading Worked

To see that lazy loading has worked, we have used a developer tool by using shift+control+j. We can see that there is an additional row added. This means that our application can reach out to the required module after we click it.


Points to Remember While Using Angular Lazy Loading

Lazy Loading improves the performance of angular applications. There are many things to keep in mind while using Lazy Loading. They are as follows:

  • You should use the load children () function. It indicates a path where the module can be loaded and used when necessary. 
  • You should pre-load all the essential resources that an application will require. This can be done using predefined services.
  • Try to keep modules and components small. If you are using a large module, it will require more memory and will be slow to work.
  • Test the performance of lazy Loading on all devices and all network devices. It would be beneficial for optimal results for user needs and specific applications.
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How Does Lazy Loading Impact SEO

How Does Lazy Loading Impact SEO

As we all know, lazy Loading is most helpful for page loading. After all, the audience can access information quickly when pages are loaded fast. This creates a positive impact on the first-time user of that site. But issues arise when you are trying to optimize for SEO.

Research states that lazy Loading impacts how the search engine crawls a site. If a page or site can't load quickly, it means that the search engine can't crawl the entire page, which intends to misunderstand or ignore the content of the page.

Regarding indexing material, lazy Loading causes certain challenges for search engines. If a search engine cannot view the complete content of a website because it is lazily loaded, it may be unable to comprehend and rank the page correctly.

So it is essential to follow best practices for implementing lazy Loading to ensure that search engines can crawl and rank the content properly. 

Properties of Lazy Loading

There are many additional properties that Lazy Loading offers like:

  • Improve performance: By loading only necessary modules or information which are on demand and are needed at that particular time can significantly improve the load time of the application.
  • Better user experience: By reducing the loading time of the application, it provides better user experience and helps users.
  • Efficient Resource Utilization: Lazy loading helps in reducing the amount of resources used in an application. 

Common Issues Occur in Angular Lazy Loading

Although there is a significant improvement in page load speed while using Lazy Loading, more is needed. Some more issues that occur in lazy Loading need to be addressed. They are like:

  • When using Lazy Loading, page accessibility becomes fast, but it may not be the case for images. There is a delay in loading images.  There are ways in which you can solve this issue:

    • Use Intersection Observer API to detect images which will be entering the viewport.
    • Use margin by setting a ‘rootMargin’ parameter.
    • Can be solved by loading an image several hundred pixels before the viewport. This can be done by adding an ‘img’ tag with the ‘loading=”lazy”’ attribute.
  • It may contain some dependency issues that may need to be resolved and will cause errors. It's essential to properly configure and note that there is no circular dependency. For example, we take two modules ‘A’ and ‘B’, where ‘A’ depends on ‘B’ and ‘B’ depends on ‘A’. 
# import module A
import { B } from './b';

# inject A in B
export class A {
  constructor(private b: B) {}

# import module B
import { A } from './a';

#inject B in A
export class B {
  constructor(private a: A) {}

We can solve this issue by adding a third module in which both of the existing modules depend.

Use Cases of Angular Lazy Loading

Here are some examples where lazy Loading has been implemented in applications:

  • E-commerce websites: An E-commerce website with multiple products may use lazy Loading to improve performance. For example, the categories are lazily loaded because the user can see the data for the current category and choose what user wants rather than loading all category data at once.
  • Social media applications: A social media application has a lot of data to display. It may create some problems for the user to search for something. If a user wants to access the chat, then in that case by loading the chat module only will improve the performance of the application. Rather than all other modules at onces.
  • Enterprise application: In an enterprise application, there are different modules available, and to optimize the performance, lazy Loading should only load modules that are needed at a given time.

Benefits of Lazy Loading in Angular

Lazy Loading in Angular offers benefits that will make your site more user-friendly. They are like:

  • Fast Loading time: Using only necessary modules and components will use less time to load and thus making it fast for users to use. It will also create a positive impression on the user.
  • Less data usage: Only essential and necessary data is used initially and gradually moving forward. It will also reduce memory usage.
  • Conserver resources: only a few resources are used in starting an application, so memory usage changes dynamically, which is more optimal.

Disadvantages of Lazy Loading in Angular

There are some disadvantages of lazy Loading in Angular. They are:

  • It adds more complexity to an application structure. It may create some problems and require additional resources for configuration.
  • If lazy Loading is implemented correctly, then only it results in a consistent user experience.
  • Debugging can be more difficult when you are using Lazy Loading as it is difficult to trace back to a specific component module.

Frequently Asked Question

How can you preload angular lazy-loaded modules for better performance?

We can use ''PreloadAllModules'' to preload all lazy loaded modules after the main application has been loaded or use a custom preload strategy to preload a specific module.

What are some common issues that arise while implementing Angular Lazy Loading?

Some problems are the incorrect configuration of lazy-loaded routes, missing or inaccurate import statements, dependency issues or images not loaded correctly, or some lags in the Loading of an image.

What are some alternatives to Angular lazy loading for improving performance?

One of the alternative ways of lazy Loading is eager Loading, where all modules are loaded during the start. Another way is also using CDN (Content delivery network).

How can you debug and troubleshoot issues related to angular Lazy Loading?

There are different ways like using Angular CLI, using Angular Router events like ''RouteConfigLoadStart'' or ''RouteConfigLoadError'', or checking for circular dependencies. These all are ways to debug or solve issues related to Lazy Loading.

How do you determine which modules or components should lazy load in an Angular application?

It can be done by analyzing their usage frequency or dependency size. Modules not in need immediately for the user experience can be loaded asynchronously. We can choose according to the module size also. If we have shared modules that consist of multiple components that can also be lazy loaded. This will reduce initial loading time. 


Lazy Loading is one technique that can improve Angular Applications performance and user experience. By using Lazy Loading, we can only import necessary resources on demand. This is very effective for memory usage; it even reduces network latency and helps in fasting the load of the page. Overall, Angular Lazy Loading is valuable in the Angular developer's toolkit for building fast and efficient applications.

In this article we get to know about different aspects of Angular Lazy Loading like its use cases, its features, its working viewpoint and many more . 
To learn more about this topic do visit the link



-Introduction To AngularJs

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