Dany Paredes for This is Angular

Posted on Apr 13, 2023 • Edited on Jun 1, 2023 • Originally published at danywalls.com

Why and When Use Ng-template, NgContent, and NgContainer in Angular

#angular #javascript #frontend #programming

When I started to play with templates and dynamic content in angular, I get surprised by multiple directives in angular to work with it ng-template, ng-container, and ng-content. Each one is pretty similar initially; each has exceptional use cases and features that set them apart.

I'll be showcasing various scenarios for ng-template, ng-container, and ng-content, complete with helpful examples to illustrate the appropriate use of each directive. But first, let's briefly explain each one:

ng-template help to define a template that can be reused multiple times within an Angular component.
ng-container when we need to group elements without adding additional nodes to the DOM.
ng-content is used to render content dynamically that is passed in from the parent component.

ng-template

ng-template defines a template block that can be used to render content dynamically. It provides a way to define an HTML code that can be reused multiple times within an Angular component.

For example, one everyday use case for ng-template is to render conditional content with ngIf or ngSwitch directives.

<ng-template #myTemplate>
  <div *ngIf="hasBalance">
    <p>Your amount is 5000€.</p>
  </div>
  <div *ngIf="!hasBalance">
    <p>Sorry, no balance.</p>
  </div>
</ng-template>

In this example, we define a template block that contains two div elements with *ngIf directives. The *ngIf directives will render one of the div elements based on the value of hasBalance.

Also, we can use this template block in multiple places within our component in a ng-container element:

<ng-container *ngTemplateOutlet="myTemplate"></ng-container>

ng-container

ng-container help to group elements without adding additional nodes to the DOM. It is often used with structural directives like *ngIf, *ngFor, and *ngSwitch.

One common use case for ng-container is to apply a structural directive to multiple elements without wrapping them in an additional HTML tag for example:

  <div *ngIf="hasBalance">
    <p>Your amount is 5000€.</p>
  </div>
  <div *ngIf="!hasBalance">
    <p>Sorry, no balance.</p>
  </div>

In this example, we have two div elements with *ngIf directives. However, if we wanted to apply the *ngIf directive to both elements, we would need to wrap them in an additional HTML tag like this:

<div *ngIf="activeSession">
  <div *ngIf="hasBalance">
    <p>Your amount is 5000€.</p>
  </div>
  <div *ngIf="!hasBalance">
    <p>Sorry, no balance.</p>
  </div>
</div>

The extra div element is not necessary. Instead, we can use an ng-container element to group the div elements together without adding a tag:

<ng-container *ngIf="activeSession">
  <div *ngIf="hasBalance">
    <p>Your amount is 5000€.</p>
  </div>
  <div *ngIf="!hasBalance">
    <p>Sorry, no balance.</p>
  </div>
</ng-container>

We use the ng-container Group the div\ elements together without adding an HTML tag.

ng-content

ng-content is an easy way to dynamically render content passed in from the parent component. It allows a parent component to inject content into a child component's template.

One common use case for ng-content is to create a reusable component that can accept different content based on usage. For example:

@Component({
  selector: 'app-alert',
  template: `
    <div class="alert alert-{{type}}">
      <ng-content></ng-content>
    </div>
  `
})
export class AlertComponent {
  @Input() type: string;
}

We define an AlertComponent accepts a type input and uses ng-content to render the content passed in from the parent component. The parent component can use this component like this:

<app-alert type="success">
  <p>Success!</p>
</app-alert>

<app-alert type="danger">
  <p>Something went wrong!</p>
</app-alert>

In this example, we use them AlertComponent to display success and error messages. The content inside the component is injected into the template using ng-content.

Conclusion

In conclusion, ng-template, ng-container, and ng-content are three commonly used directives in Angular templates. Although they may appear similar initially, each one has a unique purpose and function.

I hope these examples and scenarios assist you in selecting and utilizing each one as needed.

Photo by Kelly Sikkema on Unsplash