Exploring the New Angular 17 @if() and @for() Directives

4 min. read

Angular, a popular JavaScript framework, continues to evolve, offering developers powerful tools to build dynamic and interactive web applications. Among its many features, Angular 17 introduces the @if() and @for() "block" directives, which streamline the development process and enhance code readability. They also offer performance enhancements compared to their predecessors, *ngIf and *ngFor. Let's dive into how these directives improve performance within internal algorithms, providing a smoother experience for developers and end-users.

What are Angular @if() and @for() Directives?

In Angular, directives are markers on a DOM element that tell Angular's HTML compiler to attach a specified behavior to that element or even transform the DOM element and its children. The @if() and @for() directives are structural directives, meaning they change the structure of the DOM.

  • @if() Directive: The @if() directive conditionally includes or excludes a template based on the evaluation of an expression. If the expression evaluates to true, the template is rendered; otherwise, it is removed from the DOM.
  • @for() Directive: The @for() directive repeats a portion of the template multiple times based on the iteration over a collection. It's akin to a traditional for loop, allowing developers to iterate over arrays or other iterable objects and render a template for each item.

Benefits of Angular @if() Directive

  1. Conditional Rendering: With the @if() directive, developers can easily conditionally render parts of the UI based on certain conditions. This simplifies the logic required for showing or hiding elements dynamically, enhancing code clarity and maintainability.
  2. Improved Performance: Elements wrapped within an @if() directive are only rendered when the associated expression evaluates to true. This can lead to better performance, as unnecessary DOM elements are not created or maintained when they're not needed.
  3. Enhanced User Experience: By selectively showing or hiding UI elements based on user interactions or application state, developers can create more tailored and intuitive user experiences, improving usability and engagement.

Performance Improvements of Angular @if() Directive

  1. Optimized Rendering Logic: The @if() directive optimizes rendering logic by efficiently managing the creation and removal of DOM elements based on conditional expressions. Unlike its predecessor *ngIf, which sometimes incurred unnecessary re-renders, Angular 17's @if() directive intelligently updates the DOM only when the condition changes, leading to faster rendering times.
  2. Reduced Change Detection Overhead: Angular's change detection mechanism is crucial for updating the UI in response to data changes. However, excessive change detection can impact performance, especially in complex applications. The @if() directive minimizes change detection overhead by selectively rendering components based on conditions, resulting in a more efficient update cycle.
  3. Scoped View Rendering: When using *ngIf, the Angular compiler creates a separate template view for each conditionally rendered element, potentially leading to a proliferation of view instances. In contrast, the @if() directive scopes the rendered content within the same view, reducing memory consumption and improving rendering performance, particularly in scenarios with frequent conditional rendering.
@if (a > b) {
  {{a}} is greater than {{b}}
} @else if (b > a) {
  {{a}} is less than {{b}}
} @else {
  {{a}} is equal to {{b}}
Syntax of @If()

Benefits of Angular @for() Directive

  1. Dynamic List Rendering: The @for() directive simplifies the process of rendering lists or collections of data. Developers can iterate over arrays, objects, or other iterable data structures, generating repetitive UI elements effortlessly.
  2. Reduced Boilerplate Code: Traditional methods of iterating over collections in Angular often required verbose code, especially for complex data structures. The @for() directive reduces boilerplate code, resulting in cleaner and more concise templates.
  3. Flexibility and Expressiveness: Whether you're rendering a simple list of items or generating complex nested structures, the @for() directive offers the flexibility to handle various scenarios with ease. Developers can leverage Angular's powerful template syntax within the loop to customize each iteration according to their requirements.

Performance Enhancements of Angular @for() Directive

  1. Efficient Iteration Handling: Iterating over collections using the @for() directive offers performance improvements over *ngFor due to optimized iteration handling algorithms. Angular 17's compiler leverages more efficient iteration strategies, resulting in faster rendering of repetitive UI elements, especially in scenarios involving large datasets or nested iterations.
  2. Minimized Template Fragmentation: In complex templates with nested *ngFor loops, the previous *ngFor directive could lead to template fragmentation, resulting in decreased rendering performance. The @for() directive addresses this issue by optimizing template rendering, reducing fragmentation, and minimizing the overhead associated with rendering nested iterations.
  3. Streamlined Change Detection: Angular's change detection process is integral to detecting and propagating data changes throughout the application. By optimizing change detection algorithms for @for() directives, Angular 17 minimizes the computational overhead associated with detecting changes within iterated elements, leading to improved overall performance, especially in scenarios with frequent data updates.
@for (item of items; track {
  <li> {{ }} </li>
} @empty {
  <li> There are no items. </li>
Syntax of @for()

Final Thoughts

The introduction of @if() and @for() directives in Angular 17 significantly benefits developers by simplifying common tasks and enhancing the flexibility and expressiveness of Angular templates. These directives allow developers to write cleaner, more readable code and build dynamic and interactive web applications more efficiently.

The Angular 17 @if() and @for() directives enhance code readability and maintainability and offer significant performance improvements over their predecessors, *ngIf and *ngFor. Furthermore, these directives implement algorithm optimizations for rendering, change detection, and iteration handling, contributing to a smoother and more efficient Angular development experience. Thus, developers can build faster, more responsive web applications, ultimately delivering a better user experience.

If you have more questions about these directives or just want to share additional thoughts on the latest Angular release, we'd love to hear from you! Reach us via Twitter, Linkedin, or send us a message.

Kim Pham

Senior Front-end Web Developer