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In this article we will cover on how to implement how to create custom directive in angular 9/8. we will help you to give example of angular 9 custom directives example. We will look at example of angular 9/8 create custom directive example. let’s discuss about custom directive in angular 9 example. Alright, let’s dive into the steps.

In this tutorial, i will explain you how to custom attribute directive in angular 9/8 application. Angular attribute directive can be simply described as a component without any template. instead of it is directly using the element it is applied to. you don't have to write too many code for html element, you can simply create custom attribute with some logical and you can easily reuse it with other element too.

In this example, we will create appBtn directive. in this directive we will add two event one is mouseenter and mouseleave. using that event will change color of button font. i will take one button and we will add appBtn attribute.

So, let's see bellow step to creating custom directive in angular 9.

Step 1: Create New App

You can easily create your angular app using bellow command:

ng new my-module-app

Step 2: Create Custom Directive

After creating successfully app, we need to create directive using angular cli command. angular provide command to create directive in angular application. so let's run bellow command to create admin module:

ng generate directive btn

now they created btn.directive.ts and in this file we will write code for custom directive. we will import ElementRef, Renderer2 and HostListener. we will also write mouseenter and mouseleave event. so let's update as like bellow:

src/app/btn.directive.ts

import { Directive, ElementRef, Renderer2, HostListener } from '@angular/core';
  
@Directive({
  selector: '[appBtn]'
})
export class BtnDirective {
  
  constructor(
    private elementRef: ElementRef, 
    private renderer: Renderer2
    ) {
        this.setFontColor('red')
  }
  
  setFontColor(color: string) {
    this.renderer.setStyle(
      this.elementRef.nativeElement,
      'color',
      color
    )
  }
  
  @HostListener('mouseenter') onMouseEnter() {
    this.setFontColor('blue')
  }
  
  @HostListener('mouseleave') onMouseLeave() {
    this.setFontColor('red')
  }
  
}

Step 3: Import Module to module.ts file

In last step, we will simply import BtnDirective to module.ts file, so, let's update that file as like bellow:

src/app/app.module.ts

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { FormsModule } from '@angular/forms';
  
import { AppComponent } from './app.component';
import { BtnDirective } from './btn.directive';
  
@NgModule({
  imports:      [ BrowserModule, FormsModule ],
  declarations: [ AppComponent, BtnDirective ],
  bootstrap:    [ AppComponent ]
})
export class AppModule { }

Step 4: Update Component HTML File

here, we have to update our app component html file, we need to add simple button with custom directive, so let's update it as like bellow:

src/app/app.component.html

<button appBtn>My Button</button>

Now we are ready to run our example, you can run by following command:

ng serve

I hope it can help you...