Angular Conditional Class with *ngClass

In this article, we will see the basic implementation of the Conditional class with *ngClass in Angular, along with understanding their implementation with the help of examples.

Conditional class with *ngClass

Angular's *ngClass directive allows us to apply CSS classes conditionally to an element. It provides a convenient way to dynamically toggle classes based on specific conditions. With *ngClass, we can bind a class name or an object to an element and specify the conditions under which the class should be applied. The directive evaluates the expressions and adds or removes the specified classes accordingly. This feature is particularly useful when you want to apply different styles or behavior to an element based on certain conditions, such as user interactions, data states, or dynamic variables. Overall, *ngClass simplifies the process of adding or removing classes dynamically, making it easier to create responsive and interactive Angular applications.

Syntax:

// String expression
<div [ngClass]="'class-name'"></div> // Array expression
<div [ngClass]="['class1', 'class2']"></div>  // Object expression
<div [ngClass]="{ 'class1': condition1, 'class2': condition2 }"></div> // Mixed expression
<div [ngClass]="['class1', { 'class2': condition }]"></div>

There are various aspects where the *ngClass is beneficial to implement. A few of them are described below:

• Boolean Properties: Define boolean properties in your component class and use them in the *ngClass expression. Set these properties to true or false based on your conditions to toggle the classes.

<div [ngClass]="{ 'active': isActive, 'highlight': isHighlighted }"></div>

• String Expressions: If you have a static class name or want to apply a class directly based on a condition, you can use a string expression directly in the *ngClass directive.

<div [ngClass]="isActive ? 'active' : 'inactive'"></div>

• Array Expressions: Use an array expression when you want to apply multiple classes conditionally. Combine static class names and class names based on conditions within the array.

<div [ngClass]="['active', isHighlighted ? 'highlight' : '']"></div>

• Object Expressions: Use an object expression when you have multiple classes and conditions. The key represents the class name, and the value represents the condition to apply that class.

<div [ngClass]="{ 'active': isActive, 'highlight': isHighlighted }"></div>

We can also use other directives like *ngIf or *ngFor along with *ngClass to conditionally apply classes based on changing states or data conditions.

Approach 1:

In this approach, when the button is clicked, it toggles the value of the "isClicked" variable and updates the message accordingly. If "isClicked" is true, the message displays "Welcome to GFG!!!" by changing the styling of the message with the help of *ngClass; otherwise, it displays nothing. The ngClass directive is used to conditionally apply the "text-darkgreen" class to the message element based on the value of "isClicked".

Example: This example illustrates the implementation of a Conditional class with *ngClass in Angular.

• app.component.html

<div class="container">
    <div class="row">
        <div class="col-xs-12">
            <h2>Geeks For Geeks</h2>
            <button class="btn btn-primary"
                    (click)="getMessage()">
                  Click Me
              </button>
            <b>
                <h3 class="display" 
                    [ngClass]="{'text-darkgreen':  isClicked}">
                    {{message}}
                </h3>
            </b>
        </div>
    </div>
</div>

• app.component.css

h2 {
    color: darkgreen;
}

.text-darkgreen {
    color: white;
    font-size: medium;
    width: 350px;
    padding: 20px;
    background: green;
}

• app.component.ts

import { Component } from '@angular/core';

@Component({
    selector: 'app-root',
    templateUrl: './app.component.html',
    styleUrls: ['./app.component.css'],
})
export class AppComponent {
    message: string = '';
    isClicked = false;
    getMessage() {
        this.isClicked = !this.isClicked;
        if (this.isClicked) {
            this.message = 'Welcome to GFG!!!';
        } else {
            this.message = '';
        }
    }
}

Output:

Approach 2:

In this approach, It contains a user interface with three buttons: "Toggle Success," "Toggle Error," and "Toggle Warning." When a button is clicked, it triggers a corresponding function that changes the styling of the message that has been displayed accordingly with the help of *ngClass. The message is then displayed in an h3 element with a CSS class based on the active state. This allows for toggling between success, error, and warning messages dynamically.

Example: In this example, we are implementing the Conditional class with *ngClass in Angular, where the 3 toggle buttons are added that will render the message dynamically depending on the type of action.

• app.component.html

<div class="container">
    <div class="row">
        <div class="col-xs-12">
            <h2>Welcome to GFG!!!</h2><br>
            <button class="btn btn-success"
                    (click)="Success()">
                  Toggle Success
              </button>  
            <button class="btn btn-danger" 
                    (click)="Error()">
                  Toggle Error
              </button> 
            <button class="btn btn-warning" 
                    (click)="Warning()">
                  Toggle Warning
              </button> 
            <h3 class="display" 
                [ngClass]="{ 'Success': isSuccess, 
                             'Error': isError ,  
                             'Warning':isWarning}">
                {{message}}
            </h3>
        </div>
    </div>
</div>

• app.component.css

h2 {
    color: darkgreen;
}

.Success {
    color: black;
    font-size: medium;
    width: 350px;
    padding: 20px;
    background: lightgreen;
}

.Error {
    color: black;
    font-size: medium;
    width: 350px;
    padding: 20px;
    background: red;
}

.Warning {
    color: black;
    font-size: medium;
    width: 350px;
    padding: 20px;
    background: yellow;
}

• app.component.ts

import { Component } from '@angular/core';

@Component({
    selector: 'app-root',
    templateUrl: './app.component.html',
    styleUrls: ['./app.component.css'],
})
export class AppComponent {
    isSuccess: boolean = false;
    isError: boolean = false;
    isWarning: boolean = false;
    message: string = '';

    Success() {
        this.isSuccess = true;
        this.isError = false;
        this.isWarning = false;
        this.message = 'Success Clicked!';
    }

    Error() {
        this.isError = true;
        this.isSuccess = false;
        this.isWarning = false;
        this.message = 'Danger Clicked!!';
    }

    Warning() {
        this.isWarning = true;
        this.isError = false;
        this.isSuccess = false;
        this.message = 'Warning Clicked!!';
    }
}

Output: