Angular directives are a powerful feature that allows developers to extend HTML functionality, modify element behavior, and build reusable components. If you're preparing for Angular interview questions or looking to strengthen your grasp on directives, this guide will walk you through the fundamentals, types of directives, and frequently asked interview questions.
A directive in Angular is a special class that enhances the behavior of elements in the DOM. Directives can modify an element’s structure, appearance, or functionality, making them a crucial part of Angular development.
Angular provides three main types of directives:
Component Directives
Components are the most commonly used directives in Angular.
They are essentially directives with an associated template and styles.
Structural Directives
These directives modify the structure of the DOM.
Examples include *ngIf (for conditional rendering), *ngFor (for loops), and *ngSwitch (for dynamic content display).
Attribute Directives
Used to change the appearance or behavior of an element without altering its structure.
Examples include ngClass (for dynamically applying CSS classes) and ngStyle (for inline styling).
A component is a directive that comes with a template, styles, and encapsulated logic, while a directive is primarily used to modify existing elements. Components are declared using @Component, whereas directives use @Directive.
Structural directives dynamically modify the DOM by adding or removing elements. They are typically prefixed with an asterisk (*).
*ngIf renders elements based on a condition.
*ngFor loops over a collection and generates elements dynamically.
*ngSwitch controls multiple elements based on a given expression.
Attribute directives modify the appearance or behavior of an element without affecting the DOM structure.
ngClass dynamically applies CSS classes based on conditions.
ngStyle allows inline styles to be applied dynamically.
Developers can also create custom attribute directives to enhance user interactions, such as adding hover effects or dynamic styles.
To create a custom directive in Angular, follow these steps:
Use the Angular CLI command:
ng generate directive directive-name
Implement the directive’s logic in the generated TypeScript file.
Custom directives can be used to change element properties, listen for user interactions, or apply dynamic styles.
@HostListener listens to events on the host element and executes a method when an event occurs.
@HostBinding binds a property of the directive to a property of the host element, allowing dynamic styling or class changes.
For example, @HostListener can be used to detect mouse hover and change the background color of an element dynamically, while @HostBinding can apply CSS styles dynamically based on certain conditions.
Both ngClass and ngStyle help with dynamic styling, but they work differently:
ngClass allows multiple CSS classes to be applied dynamically.
ngStyle applies inline styles directly to an element.
For example, ngClass is useful for toggling themes or highlighting active elements, while ngStyle is commonly used to adjust styles such as color, font size, or padding dynamically.
Angular directives are essential for building dynamic, reusable, and flexible components. Understanding structural directives, attribute directives, and custom directives will not only improve your Angular development skills but also help you excel in Angular interview questions.