Angular Built-in Directives

Angular provides a set of built-in directives to help developers manipulate the DOM (Document Object Model) dynamically in response to user input or changes in the application state. Directives are special instructions that tell Angular how to transform the HTML DOM. This article will cover some of the most commonly used Angular directives, including syntax, examples, output, explanation, use cases, important points, and summary.

Syntax

The syntax for using Angular directives is as follows:

<tag-name directive-name="[expression]"></tag-name>

The tag-name is the element to which the directive is applied, and the directive-name is the name of the directive.

Examples and Output

NgIf

The ngIf directive is used to conditionally add or remove content from the DOM based on a boolean expression.

<p *ngIf="showText">This is text to be shown</p>

In this example, the content inside the paragraph element will be displayed only if showText is true.

NgFor

The ngFor directive is used to loop over a collection of data and create multiple instances of a template.

<ul>
  <li *ngFor="let item of items">{{ item }}</li>
</ul>

In this example, the ngFor directive is used to iterate over the items array and create an li element for each item.

NgClass

The ngClass directive is used to conditionally apply CSS classes to an element based on an expression.

<p [ngClass]="{ 'text-green': isGreen, 'text-large': isLarge }">This is some text</p>

In this example, the ngClass directive is used to add the text-green and text-large CSS classes to the p element based on the isGreen and isLarge boolean expressions.

NgStyle

The ngStyle directive is used to conditionally apply CSS styles to an element based on an expression.

<div [ngStyle]="{ 'background-color': bgColor, 'color': textColor }">This is some text</div>

In this example, the ngStyle directive is used to set the background-color and color CSS properties of the div element based on the bgColor and textColor expressions.

Explanation

Angular directives are markers on a DOM element that tell Angular to perform a specific operation. The content in between the opening and closing tags of the directive is evaluated as a JavaScript expression and the result is used to dynamically modify the DOM.

Use Cases

Angular directives can be used in a variety of scenarios, including:

• Conditionally showing or hiding content
• Looping through collections and generating multiple instances of a template
• Applying dynamic styles and classes based on the state of the application
• Interacting with user input events such as click, hover, and submit

Important Points

• Angular directives are prefixed with the ng prefix to distinguish them from custom directives.
• The * prefix before an Angular directive is a shorthand for the ng-template element.
• Angular directives can be combined and nested to build complex templates that dynamically update based on the application state.

Summary

Angular provides a rich set of built-in directives that allow developers to easily manipulate the DOM based on the application state. Understanding the syntax, use cases, and important points for these directives is critical to building powerful and responsive web applications with Angular.