Angular, one of the most popular web development frameworks, is about to release its latest version, Angular 17, in the beginning of November. This version comes with an exciting new feature called deferred loading (RFC), which aims to further enhance the performance and user experience of Angular applications. In this article, we'll dive into the concept of deferred loading and its key aspects in Angular 17.

Understanding Deferred Loading

Deferred loading is a technique that allows web applications to load resources, such as scripts and components, only when they are needed. Unlike traditional loading, where all content is fetched upfront during the initial page load, deferred loading defers the loading of non-essential content until specific conditions are met. These conditions can include user interactions, scrolling, or reaching a particular point in the page.

The primary benefit of deferred loading is that it significantly improves the user experience. By reducing the initial page load time, users can start interacting with the application sooner. Meanwhile, non-essential parts of the app load in the background. This not only makes the application feel faster but also conserves bandwidth and reduces server load.

Evolution of Lazy Loading in Angular

In previous versions of Angular, lazy loading was possible through the router or dynamic imports in combination with ngComponentOutlet. However, Angular 17 takes lazy loading to the next level with the introduction of the @defer control block.

With Angular 17's @defer block, you can enable lazy-loading of content within the block. What's even more remarkable is that lazy loading now extends to the dependencies of the content within the block. This includes components, directives, and pipes, which will also be lazy-loaded.

Key Aspects of Deferred Loading in Angular 17

Angular 17's deferred loading introduces several key aspects that developers can leverage to optimize their applications. Let's explore some of these features:

1. Logical Expression Trigger:

You can specify a logical expression to trigger the rendering of a deferred block. For example:

html

@defer (when isCheckedDefer())

2. Declarative Trigger Conditions:

• Angular 17 supports declarative trigger conditions, including:
• on interaction
• on hover
• on idle
• on timer
• on viewport

3. Placeholder, Loading, and Error States:

You can define placeholder, loading, and error states with @placeholder, @loading, and @error blocks. This helps provide feedback to users during the loading process.

4. Prefetching:

In addition to trigger conditions, Angular 17 allows you to specify prefetch conditions, optimizing performance further.

Exploring Declarative Trigger Conditions

Declarative trigger conditions in Angular 17 provide developers with granular control over when deferred loading should occur.

For example, with "on interaction," the deferred block is rendered when the user interacts with its associated placeholder. This interaction can be triggered by a click, touch, focus, or input events like keypress.

• Similarly, "on hover" triggers the deferred block when the user hovers over its placeholder, creating an immersive user experience.
• "on idle" allows the deferred block to be loaded when the browser reaches an idle state after the page has been loaded. This is a great way to optimize performance during periods of inactivity.
• The "on timer" condition allows you to specify a time delay before rendering the deferred block. This can be helpful for scenarios where you want content to appear after a certain period.
• Finally, "on viewport" triggers the deferred block when the associated placeholder enters the browser's viewport, ensuring that content is loaded precisely when it's about to become visible.
   

Prefetching for Improved Performance

One of the exciting aspects of Angular 17's deferred loading is the ability to specify prefetch conditions. This means you can optimize your application's performance by loading content even before it's needed, based on specified conditions.

In summary, Angular 17's deferred loading is a game-changer in terms of optimizing web application performance and user experience. With the flexibility to trigger loading based on various conditions and the option to prefetch content, developers can create highly efficient applications.

As Angular 17 is set to be released in the near future, these features are bound to reshape the way we build Angular applications. Get ready to explore the potential of deferred loading and take your web development projects to the next level with Angular 17.