Angular Directives: Now Enhance Your Angular App UI Easily

Angular Directives

Angular Directives are one of Angular's key building components, allowing you to create dynamic, reusable components. Just Imagine you're developing an Angular app and need additional control over how your HTML behaves or interacts with the user. This is where Angular Directives come into play! In Angular, directives make your forms dynamic. They are essentially the secret sauce that allows you to extend HTML beyond its default capabilities, and believe me, once you start utilizing them, you'll understand how much they can simplify your code.

In this Angular Tutorial, I am gonna show you how Angular Directives works on UI along with HTML, We will learn What are Directives in Angular, the Types of Directives in Angular, and many more.

What are Directives in Angular?

Angular directives are essential elements of Angular apps. They are special markup tokens that instruct the Angular framework to act on a DOM element. Directives can be used to do a range of things, including altering the DOM, adding behavior to elements, and controlling the layout of a web application. They allow developers to reuse angular components and expand HTML syntax to construct dynamic and interactive online apps.

Types of Directives in Angular

There are 4 Types of Directives in Angular:

1. Component Directives
2. Attribute Directives
3. Structural Directives
4. Custom Directives

You can see that here we explained the different types of directives in Angular with examples.

1. Components Directives

The directive with a template specification and this type of directive is the most common directive type in Angular. Typically, a Component is a directive with a template. @Component decorator extends the @Directive decorator with template-oriented features. A component class is declared using the @Component decorator. @Component decorator contains metadata about the component i.e. selector, templateURL, styleUrls, etc.

Example of Component Directive

import {Component} from '@angular/core' 
 
@Component({
  selector: 'app-hello',
  template: `<h1>Hello, World!</h1>})
 
export class AppComponent{}

Explanation

Here, "AppComponent" is a component directive that displays "Hello, World!" on the UI. Component directives have their own lifecycle hooks and are fundamental to Angular’s architecture. This code imports the Component class from the Angular core library and creates an Angular component called AppComponent. The @Component decorator specifies details about the component, such as its HTML template and styles.

2. Attribute Directive

The directive that changes the appearance or behavior of an element, component, or other directives. Attribute directives are used to change the appearance or behavior of an existing DOM element. ngStyle and ngClass are the commonly used examples for attribute directives. Exploring attribute directives is an essential part of Angular JS training.

NgStyle

This is used to configure multiple inline styles for HTML elements.

1. Setting inline styles with NgStyle

 import { Component } from '@angular/core'; 
 
 @Component({ 
 selector: 'Satya-App', 
 template: `<button style='color:green' [ngStyle]="MyStyle()">Satyaprakash Samantaray</button>`
 }) 
 export class AppComponent { 
 isBold: boolean = true; 
 fontSize: number = 30; 
 isItalic: boolean = true; 
 
 MyStyle() { 
 let mystyles = { 
 'font-weight': this.isBold ? 'bold' : 'normal', 
 'font-style': this.isItalic ? 'italic' : 'normal', 
 'font-size.px': this.fontSize 
 }; 
 
 return mystyles; 
 } 
 } 

Explanation

Here I added a button control in the template part with a style sheet named MyStyle(). This MyStyle CSS method is defined as below.

 MyStyle() { 
 let mystyles = { 
 'font-weight': this.isBold ? 'bold' : 'normal', 
 'font-style': this.isItalic ? 'italic' : 'normal', 
 'font-size.px': this.fontSize 
 }; 

 return mystyles;

Output

2. Usage of NgStyle in your component

currentStyles: Record = {};
/* . . . */
setCurrentStyles() {
  // CSS styles: set per current state of component properties
  this.currentStyles = {
    'font-style': this.canSave ? 'italic' : 'normal',
    'font-weight': !this.isUnchanged ? 'bold' : 'normal',
    'font-size': this.isSpecial ? '24px' : '12px',
  };
}

Explanation

<div [ngStyle]="currentStyles">
  This div is initially italic, normal weight, and extra large (24px).
</div>

NgClass

Example for NgClass

 import { Component } from '@angular/core'; 
 
 @Component({ 
 selector: 'Satya-App', 
 template: `<button class='colorClass' [ngClass]='applyClasses()'>Satyaprakash Samantaray</button>`, 
 styles: [`.boldClass{ 
 font-weight:bold; 
 font-size : 30px; 
 } 
 
 .italicsClass{ 
 font-style:italic; 
 } 
 
 .colorClass{ 
 color:Red; 
 }`] 
 }) 
 export class AppComponent { 
 applyBoldClass: boolean = true; 
 applyItalicsClass: boolean = true; 
 
 applyClasses() { 
 let classes = { 
 boldClass: this.applyBoldClass, 
 italicsClass: this.applyItalicsClass 
 }; 
 
 return classes; 
 } 
 } 

Explanation

In this NgClass we are using the class attribute of the HTML element to apply styles.

 template: `<button class='colorClass' [ngClass]='applyClasses()'>Satyaprakash Samantaray</button>`,

Output

3. Structural Directive

The directive changes the DOM layout by adding or removing the DOM elements. Structural directives are used to alter the layout by adding, removing, and replacing elements in the DOM. Asterisk (*) is used when these directives are used with the HTML elements. *ngIf, *ngFor, *ngSwitch are some commonly used structural directives in angular.

1. NgIf

It is used to create or remove a part of the DOM tree depending on a condition.

Example for ngIf

 import { Component } from '@angular/core'; 
 
 @Component({ 
 selector: 'Satya-App', 
 template: `<div style='color:blue' *ngIf="true">You can See Satyaprakash....</div>`
 }) 
 export class AppComponent { 
 
 } 

Here If ngif= true So, the text will be visible on the web page.

  template: `<div style='color:blue' *ngIf="true">You can See Satyaprakash....</div>`

Output

2. NgFor

Example for ngFor: TS Code

import { Component } from '@angular/core'; 
 
 @Component({ 
 selector: 'Satya-App', 
 templateUrl: './app.component.html', 
 }) 
 export class AppComponent { 
 employees: any[] = [ 
 { 
 code: '1001', name: 'Satya', gender: 'Male', 
 annualSalary: 5500, dateOfBirth: '25/6/1988' 
 }, 
 { 
 code: '1002', name: 'Mohit', gender: 'Male', 
 annualSalary: 5700.95, dateOfBirth: '9/6/1982' 
 }, 
 { 
 code: '1003', name: 'Rohit', gender: 'Male', 
 annualSalary: 5900, dateOfBirth: '12/8/1979' 
 }, 
 { 
 code: '1004', name: 'Satyaprakash Samantaray', gender: 'Female', 
 annualSalary: 6500.826, dateOfBirth: '14/10/1980' 
 }, 
 ]; 
 } 

Explanation

I have created a class named employees and inserted values into its corresponding properties.

 employees: any[] = [ 
 { 
 code: '1001', name: 'Satya', gender: 'Male', 
 annualSalary: 5500, dateOfBirth: '25/6/1988' 
 },

Example for ngFor: HTML Code

 <!DOCTYPE html> 
 <html> 
 <head> 
 <title></title> 
 <meta charset="utf-8" /> 
 <style> 
 table { 
 font-family: arial, sans-serif; 
 border-collapse: collapse; 
 width: 100%; 
 } 
 
 td, th { 
 border: 1px solid #dddddd; 
 text-align: left; 
 padding: 8px; 
 } 
 
 tr:nth-child(even) { 
 background-color: #dddddd; 
 } 
 </style> 
 </head> 
 <body> 
 <table align="center" border="1" cellpadding="4" cellspacing="4"> 
 <thead> 
 <tr> 
 <th style="background-color: Yellow;color: blue">Code</th> 
 <th style="background-color: Yellow;color: blue">Name</th> 
 <th style="background-color: Yellow;color: blue">Gender</th> 
 <th style="background-color: Yellow;color: blue">Annual Salary</th> 
 <th style="background-color: Yellow;color: blue">Date of Birth</th> 
 </tr> 
 </thead> 
 <tbody> 
 <tr *ngFor='let employee of employees'> 
 <td>{{employee.code}}</td> 
 <td>{{employee.name}}</td> 
 <td>{{employee.gender}}</td> 
 <td>{{employee.annualSalary}}</td> 
 <td>{{employee.dateOfBirth}}</td> 
 </tr> 
 <tr *ngIf="!employees || employees.length==0"> 
 <td colspan="5"> 
 No employees to show in the page.... 
 </td> 
 </tr> 
 </tbody> 
 </table> 
 </body> 
 </html> 

Here NgFor is used to display a list of items using repetitive loops that are data of the employee's class.

 <tr *ngFor='let employee of employees'> 
 <td>{{employee.code}}</td> 
 <td>{{employee.name}}</td> 
 <td>{{employee.gender}}</td> 
 <td>{{employee.annualSalary}}</td> 
 <td>{{employee.dateOfBirth}}</td> 
 </tr> 

Output

3. NgSwitch

app.component.ts with NgSwitch implementation

 import { Component } from '@angular/core'; 
 
 @Component({ 
 selector: 'Satya-App', 
 template: `<h2>{{title}}</h2> 
 <p *ngIf="showElement">Show Element</p> 
 <div [ngSwitch]="inpvalue"> 
 <p style='color:blue' *ngSwitchCase="1">You have selected M S Dhoni</p> 
 <p style='color:blue' *ngSwitchCase="2">You have selected Sachin Tendulkar</p> 
 <p style='color:blue' *ngSwitchCase="3">You have selected Satyaprakash Samantaray</p> 
 <p style='color:red' *ngSwitchDefault>Sorry! Invalid selection....</p> 
 </div>` 
 }) 
 export class AppComponent { 

 inpvalue: number = 3; 
 } 

You can display one element from among several possible elements, based on a switch condition. Angular puts only the selected element into the DOM. Here we are using ngswitchcase to apply switch case and ngswitch default is for invalid selection. Using the switch directive we can show output by passing the value of the pvalue property in the AppComponent class.

Output

For valid selection >>

For Invalid selection >>

You can check the code compilation status in the command prompt during a change in code using Visual Studio.

4. Custom Attribute Directive

Custom directives can also be created if any of the above directives do not solve our purpose for the requirement. Custom attribute directives can be created by using @Directive decorator. Custom attribute directives can be used to modify the background color, and text information of an HTML element, and that process is called a host element. To change the UI look angular provides an ElementRef class that can directly access DOM.

Creating a Custom Directive

Let's create a folder under an app called directives. Under directives create a file called red.directive.ts as given below:

 import { Directive, ElementRef } from '@angular/core';
 
 @Directive({ 
 selector: '[ColorRed]' 
 })
 export class MyCustomDirective {
 constructor(elRef: ElementRef) {
 elRef.nativeElement.style.color = 'darkred';
 }
 } 

Make a directive named as myRed directive. We can use it with HTML elements such as <p> and <div>, the text color within that element will be red. The @Directive is used as an angular directive to retrieve directive configuration metadata. To use our custom directive in our angular project follow the below code to set up in the application module.

 import { BrowserModule } from '@angular/platform-browser';
 import { NgModule } from '@angular/core';
 
 import { AppComponent } from './app.component';
 import { MyRedDirective } from './directives/red.directive';
 
 @NgModule({
 declarations: [
 AppComponent,
 MyCustomDirective
 ],
 imports: [
 BrowserModule
 ],
 providers: [],
 bootstrap: [AppComponent]
 })
 export class AppModule { }

 import { Component } from '@angular/core';
 
 @Component({
 selector: 'Satya-App',
 templateUrl: './app.component.html'
 })
 export class AppComponent { 
 txtsize = '25px';
 colors = ['red', 'blue', 'orange'];
 myColor = '';
 }

<!DOCTYPE html> 
 <html> 
 <head> 
 <title></title> 
 <meta charset="utf-8" /> 
 <style> 
 table { 
 font-family: arial, sans-serif; 
 border-collapse: collapse; 
 width: 100%; 
 } 
 
 td, th { 
 border: 1px solid #dddddd; 
 text-align: left; 
 padding: 8px; 
 } 
 
 tr:nth-child(even) { 
 background-color: #dddddd; 
 } 
 </style> 
 </head> 
 <body> 
 <p ColorRed>Custom Attribute Directive By Satyaprakash</p> 
 </body> 
 </html> 

we are ready to use our directive in the HTML template. Find the code snippet.

<body> 
 <p ColorRed>Custom Attribute Directive By Satyaprakash</p> 
 </body>

 
 import { BrowserModule } from '@angular/platform-browser';
 import { NgModule } from '@angular/core';
 
 import { AppComponent } from './app.component';
 import { MyRedDirective } from './directives/red.directive';
 
 @NgModule({
 declarations: [
 AppComponent,
 MyCustomDirective
 ],
 imports: [
 BrowserModule
 ],
 providers: [],
 bootstrap: [AppComponent]
 })
 export class AppModule { }

Here I import a custom attribute directive reference to configure the custom attribute that I have created.

  import { MyRedDirective } from './directives/red.directive';
 
 @NgModule({
 declarations: [
 AppComponent,
 MyCustomDirective
 ],

Output

Difference between structural directive and attribute directive

Structural directives are used to add, remove, and replace elements in DOM. On the other hand, attribute directives are used to change the appearance or behavior of an existing element.

Passing Input to Directives

Angular's @Input decorator allows directives to receive data from their parent components. This is how it works.

• Define a @Input property: In your directive's TypeScript code, use the @Input() decorator to indicate which property will receive data. This informs Angular that the property can be bound directly from the template.
• Pass data via property binding: In your component's HTML template, use the property binding syntax ([directiveName]="data") to bind a value from your component to the directive's @Input property.

Read More:

• Angular Developer Salary in India
• Top Angular Interview Questions and Answers

Other Directives

1. Host Listener Directive

Example: HoverTextColorDirective

// hover-text-color.directive.ts
import { Directive, ElementRef, HostListener, Renderer2 } from '@angular/core';

@Directive({
  selector: '[appHoverTextColor]'
})
export class HoverTextColorDirective {
  constructor(private el: ElementRef, private renderer: Renderer2) {}

  @HostListener('mouseenter') onMouseEnter() {
    this.changeTextColor('blue');
  }

  @HostListener('mouseleave') onMouseLeave() {
    this.changeTextColor(null);
  }

  private changeTextColor(color: string | null) {
    this.renderer.setStyle(this.el.nativeElement, 'color', color);
  }
}

<pappHoverTextColor>Hover over this text to change its color.</p>

Hovering over the paragraph turns the text color to blue.
When the mouse is released, the color returns to its default setting.

2. Input-Bound Directive

Example: DynamicFontSizeDirective

// dynamic-font-size.directive.ts
import { Directive, ElementRef, Renderer2, Input, OnChanges } from '@angular/core';

@Directive({
  selector: '[appDynamicFontSize]'
})
export class DynamicFontSizeDirective implements OnChanges {
  @Input() appDynamicFontSize: string = '16px';  // default font size

  constructor(private el: ElementRef, private renderer: Renderer2) {}

  ngOnChanges() {
    this.renderer.setStyle(this.el.nativeElement, 'font-size', this.appDynamicFontSize);
  }
}

<p [appDynamicFontSize]="'24px'">This text has a font size of 24px.</p>
<p [appDynamicFontSize]="'18px'">This text has a font size of 18px.</p>

The first paragraph’s text appears in 24px font size.
The second paragraph’s text appears in 18px font size.

import { Directive, ElementRef, HostListener, Renderer2 } from '@angular/core';
@Directive({
  selector: '[appHoverHighlight]'
})
export class HoverHighlightDirective {
  constructor(private el: ElementRef, private renderer: Renderer2) {}

  @HostListener('mouseenter') onMouseEnter() {
    this.renderer.setStyle(this.el.nativeElement, 'background-color', 'yellow');
  }

  @HostListener('mouseleave') onMouseLeave() {
    this.renderer.removeStyle(this.el.nativeElement, 'background-color');
  }
}

<p appHoverHighlight>Hover over this text to see the effect!</p>

Summary

Once we say that the components are the/ building blocks of the Angular applications, but eventually, we are saying that the directives are the building blocks of Angular applications that are used to deal with DOM elements. In this article, you learned about the various types of directives in Angular with its examples. I hope you will find it useful when you will work with your Angular Application. And wait..! if you also want to become a pro in Angular then please consider our Angular Certification Online Training plus you will get a lot of Benefits of obtaining Angular certification.

Take our Angular skill challenge to evaluate yourself!

In less than 5 minutes, with our skill challenge, you can identify your knowledge gaps and strengths in a given skill.

GET FREE CHALLENGE