In Angular component declarations, include providers, change detection, encapsulations, and hosting for optimal performance

Some packages include providers, encapsulations, changeDetections, and host in their code. What do these elements mean and how do they impact the behavior of the component class based on the following code snippet?

@Component({
    selector: 'ng-select',
    templateUrl: './ng-select.component.html',
    styleUrls: ['./ng-select.component.scss'],
    providers: [{
        provide: NG_VALUE_ACCESSOR,
        useExisting: forwardRef(() => NgSelectComponent),
        multi: true
    }],
    encapsulation: ViewEncapsulation.None,
    changeDetection: ChangeDetectionStrategy.OnPush,
    host: {
        'role': 'listbox',
        'class': 'ng-select',
        '[class.ng-select-single]': '!multiple',
    }
})

Answer №1

Here are some key concepts explained:

  • Encapsulation: If ViewEncapsulation.None is used, styles written in the styles attribute or styleUrl (css file) will have a global scope, allowing them to be used outside the component.

  • Host: Refers to adding properties directly on the host element itself. For example, in this case, it adds the ng-select role class="ng-select"

  • Providers: Services injected here will only be available at the component level. This means if there are multiple instances of ng-select, each will have its own instance of the injected class.

  • Change Detection: By configuring how change detection works on the component, you can choose when it runs. The OnPush strategy only triggers change detection on this component if any input property references have been changed.

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