Shadow DOM – How & Why? Apply Shadow DOM to Angular component

The “shadow DOM” is a concept in computer science that refers to a way of hiding the implementation details of a web component. It’s a way of creating modular, reusable components that can be used across different websites and applications, without exposing the underlying code or structure of the component.

Here’s how it works: when you create a web component, you can specify a “shadow root” that acts as a boundary between the component’s internal structure and the rest of the web page.

Anything inside the shadow root is considered part of the shadow DOM, and is hidden from the rest of the page. This means that the user of the component only sees the exposed API, and doesn’t have to worry about the details of how the component is implemented.

The shadow DOM is useful because it helps to prevent styles and scripts from the main page from leaking into the component, and vice versa.

It also allows web developers to create more modular and reusable code, which can make it easier to maintain and update complex web applications.

How to use Shadow DOM?

Here is a simple example of how the shadow DOM can be used in a web component:

<!-- This is the web component -->
<my-component>
  <h1>Hello World!</h1>
  <p>This is a simple example of a web component that uses the shadow DOM.</p>
</my-component>

<script>
  // This is the JavaScript code that defines the web component
  const template = `
    <style>
      /* This is the component's internal style sheet */
      h1 {
        color: blue;
      }
    </style>
    <h1>Hello World!</h1>
    <p>This is a simple example of a web component that uses the shadow DOM.</p>
  `;

  class MyComponent extends HTMLElement {
    constructor() {
      super();
      // Create a shadow root for the component
      this.attachShadow({mode: 'open'});
      // Add the component's template to the shadow root
      this.shadowRoot.innerHTML = template;
    }
  }

  // Register the component with the browser
  customElements.define('my-component', MyComponent);
</script>

In this example, the my-component element is a custom web component that uses the shadow DOM. The component’s internal structure and styles are hidden inside the shadow root, so that the user of the component only sees the exposed API.

This means that the user can’t see the component’s internal style element, and can’t change the component’s internal styles using CSS rules from the main page. The component’s internal styles will always be applied, regardless of the styles on the main page.

Shadow DOM in Angular

The shadow DOM is not specific to Angular, but Angular does provide support for using the shadow DOM in its components. To use the shadow DOM in an Angular component, you can use the ViewEncapsulation enum to specify the desired encapsulation strategy.

Here is an example of how this might look in an Angular component:

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

@Component({
  selector: 'my-component',
  template: `
    <h1>Hello World!</h1>
    <p>This is a simple example of an Angular component that uses the shadow DOM.</p>
  `,
  styleUrls: ['./my-component.css'],
  encapsulation: ViewEncapsulation.ShadowDom
})
export class MyComponent {
  // The component's class definition goes here
}

In this example, the MyComponent class is an Angular component that uses the shadow DOM for encapsulation. The encapsulation property of the @Component decorator is set to ViewEncapsulation.ShadowDom to enable the shadow DOM for this component.

This means that the component’s internal styles, defined in the my-component.css file, will be hidden inside the shadow root, and will not be affected by the styles on the main page. The user of the component will only see the exposed API, and will not be able to access the component’s internal styles.

Overall, the shadow DOM can be a useful tool for creating modular, reusable components in Angular. It allows you to hide the implementation details of your components, and helps to prevent styles and scripts from leaking between your components and the rest of the page.

Kent Wynn

Apply Shadow DOM in Ng-Template

In Angular, the ng-template tag is a way of defining a template that can be used in multiple places in your application. You can use the ng-template tag to define a template for a component, and then reference that template in different parts of your application using the ngTemplateOutlet directive.

Here is an example of how this might look in an Angular component that uses the shadow DOM:

import { Component, ViewEncapsulation, ViewChild, TemplateRef } from '@angular/core';

@Component({
  selector: 'my-component',
  template: `
    <h1>Hello World!</h1>
    <ng-template #myTemplate>
      <p>This is a simple example of an Angular component that uses the shadow DOM and the ng-template tag.</p>
    </ng-template>
    <div *ngTemplateOutlet="myTemplate"></div>
  `,
  styleUrls: ['./my-component.css'],
  encapsulation: ViewEncapsulation.ShadowDom
})
export class MyComponent {
  @ViewChild('myTemplate') myTemplate: TemplateRef<any>;
  
  // The component's class definition goes here
}

In this example, the my-component component uses the shadow DOM for encapsulation, and defines a template using the ng-template tag. The ngTemplateOutlet directive is then used to reference the template and render its contents in the component.

This allows you to define a template once, and then use it multiple times in your component, without repeating the same content in your component’s template.

Overall, the ng-template tag can be a useful tool for defining reusable templates in Angular, and it can be used in combination with the shadow DOM to create modular, reusable components.

Which Browsers support Shadow DOM?

The shadow DOM is supported by most modern web browsers, including recent versions of Google Chrome, Mozilla Firefox, Microsoft Edge, Apple Safari, and others. However, support for the shadow DOM is not universal, and some older or less commonly used browsers may not support it.

Here is a breakdown of the current support for the shadow DOM among different browsers, according to Can I Use:

• Google Chrome: Full support (version 63 and above)
• Mozilla Firefox: Full support (version 63 and above)
• Microsoft Edge: Full support (version 79 and above)
• Apple Safari: Full support (version 11 and above)
• Opera: Full support (version 50 and above)
• Internet Explorer: No support

As you can see, most modern browsers support the shadow DOM, but older versions of some browsers, such as Internet Explorer, do not support it. If you want to use the shadow DOM in your web application, it’s a good idea to check for browser support and provide an alternative implementation for browsers that do not support it. This will ensure that your application is accessible to as many users as possible.

To sum up…

Here are a few best practices for using the shadow DOM in your web applications:

Use the shadow DOM to create modular, reusable components:

The shadow DOM is a great tool for creating modular, reusable components that can be used across different websites and applications.

By hiding the implementation details of your components inside the shadow root, you can create components that can be easily reused and integrated into other applications.

Use the shadow DOM to prevent style leaks:

One of the main benefits of the shadow DOM is that it helps to prevent styles and scripts from leaking between your components and the rest of the page.

This is because the shadow root acts as a boundary between the component’s internal structure and the rest of the page, so styles and scripts from the main page cannot affect the component, and vice versa.

Avoid using global styles with the shadow DOM

When using the shadow DOM, it’s best to avoid using global styles that could potentially affect your components.

This is because the shadow DOM helps to isolate your components from the rest of the page, so global styles may not be applied to your components as expected.

Instead, you should use the shadow root to define the styles for your component, so that they are applied consistently and correctly.

Use the :host selector to style the component itself:

When styling a component that uses the shadow DOM, you can use the :host selector to apply styles to the component itself.

This is useful for styling the top-level element of the component, such as setting its background color or font size.

The :host selector only applies to the component itself, and will not affect the rest of the page.

Overall, the shadow DOM is a powerful tool for creating modular, reusable components in web applications. By following these best practices, you can ensure that your components are well-structured, maintainable, and consistent across different contexts.