Mastering the DOM: A Deep Dive into Angular Directives
In the Angular ecosystem, Components are the building blocks of the User Interface. However, **Directives** are the tools that breathe life into those blocks. A Directive is essentially a class that can add new behavior to the elements of your applications or modify existing behavior.
Structural vs. Attribute Directives
Understanding the distinction between these two types is fundamental to mastering Angular templates.
Structural Directives (*)
They change the DOM layout by adding and removing DOM elements.
<div *ngIf="isLoaded">Content</div>Note the asterisk (*). This is syntactic sugar for <ng-template>.
Attribute Directives ([])
They change the appearance or behavior of an element, component, or another directive.
<div [ngClass]="{'active': isActive}"></div>Typically used with property binding syntax [].
Advanced: The Power of *ngFor
When iterating over large collections, performance can become an issue. Angular's *ngFor destroys and recreates DOM elements when the reference of the iterable changes. To prevent this expensive operation for items that haven't actually changed, use trackBy.
Pro Tip: Always separate structural directives. You cannot have*ngIfand*ngForon the same element. If you need both, wrap the inner element in an<ng-container>, which does not introduce an extra level of DOM nesting.
