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Angular7 Event Binding

Angular7 Event Binding

We will discuss how Event Binding works in Angular 7, in this chapter. When a user interacts with an application in the form of a movement on the keyboard, a mouse button, or a mouse over, it produces an event. These things must be managed in order to execute some sort of action. This is where the binding of events comes into play.

To understand this better, let's consider an example.

app.component.html

<!--The content below is only a placeholder and can be replaced.-->
<div style = "text-align:center">
   <h1>Welcome to {{title}}.</h1>
</div>

<div> Months :
   <select>
      <option *ngFor = "let i of months">{{i}}</option>
   </select>
</div>
<br/>

<div>
   <span *ngIf = "isavailable; then condition1 else condition2">
      Condition is valid.
   </span>
   <ng-template #condition1>Condition is valid</ng-template>
   <ng-template #condition2>Condition is invalid</ng-template>
</div>
<button (click) = "myClickFunction($event)">
   Click Me
</button>

We have defined a button in the app.component.html file and added a function to it using the click event.

The syntax for defining a button and adding a function to it follows.

(click) = "myClickFunction($event)"

The function is defined in :app.component.ts

	
import { Component } from '@angular/core';
@Component({
   selector: 'app-root',
   templateUrl: './app.component.html',
   styleUrls: ['./app.component.css']
})
export class AppComponent {
   title = 'Angular 7';
   
   // declared array of months.
   months = ["January", "February", "March", "April", "May","June", "July", 
      "August", "September", "October", "November", "December"];
   
   isavailable = true; //variable is set to true
   myClickFunction(event) {
      //just added console.log which will display the event details in browser on click of the button.
      alert("Button is clicked");
      console.log(event);
   }
}

After clicking the button, the control should come to the application myClickFunction and a dialog box will appear, which shows the Button is clicked as shown in the following screenshot –

The styling for button is added in add.component.css –

button {
   background-color: #2B3BCF;
   border: none;
   color: white;
   padding: 10px 10px;
   text-align: center;
   text-decoration: none;
   display: inline-block;
   font-size: 20px;
}

Let us now add the onchange event to the dropdown.

The following line of code will help you add the change event to the dropdown −

app.component.html

<!--The content below is only a placeholder and can be replaced.-->
<div style = "text-align:center">
   <h1>Welcome to {{title}}.</h1>
</div>

<div> Months :
   <select (change) = "changemonths($event)">
      <option *ngFor = "let i of months">{{i}}</option>
   </select>
</div>
<br/>

<div>
   <span *ngIf = "isavailable; then condition1 else condition2">
      Condition is valid.
   </span>
   <ng-template #condition1>Condition is valid</ng-template>
   <ng-template #condition2>Condition is invalid</ng-template>
</div>
<br/>

<button (click) = "myClickFunction($event)">
   Click Me
</button>

The function is declared in the app.component.ts file −


import { Component } from '@angular/core';
@Component({
   selector: 'app-root',
   templateUrl: './app.component.html',
   styleUrls: ['./app.component.css']
})
export class AppComponent {
   title = 'Angular 7';
   
   // declared array of months.
   months = ["January", "Feburary", "March", "April", "May", "June", "July", 
      "August", "September", "October", "November", "December"];
   
   isavailable = true; //variable is set to true
   myClickFunction(event) {
      //just added console.log which will display the event 
      details in browser on click of the button.
      alert("Button is clicked");
      console.log(event);
   }
   changemonths(event) {
      console.log("Changed month from the Dropdown");
      console.log(event);
   }
}

Pick a month from the dropdown and you will see the console message "Changed month from the dropdown" displayed along with the event in the console.

Let us add an alert message in app.component.ts when the value from the dropdown is changed as shown below −


import { Component } from '@angular/core';
@Component({ 
   selector: 'app-root', 
   templateUrl: './app.component.html', 
   styleUrls: ['./app.component.css'] 
}) 
export class AppComponent { 
   title = 'Angular 7'; 
   
   // declared array of months. 
   months = ["January", "February", "March", "April", "May", "June", "July", 
      "August", "September", "October", "November", "December"]; 
   
   isavailable = true; //variable is set to true 
   myClickFunction(event) { 
      //just added console.log which will display the event 
      details in browser on click of the button. 
      alert("Button is clicked"); console.log(event); 
   } 
   changemonths(event) { 
      alert("Changed month from the Dropdown");
   } 
}