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View encapsulation

In Angular, component CSS styles are encapsulated into the component's view and don't affect the rest of the application.

To control how this encapsulation happens on a per component basis, you can set the view encapsulation mode in the component metadata. Choose from the following modes:

  • ShadowDom view encapsulation uses the browser's native shadow DOM implementation (see Shadow DOM on the MDN site) to attach a shadow DOM to the component's host element, and then puts the component view inside that shadow DOM. The component's styles are included within the shadow DOM.

  • Emulated view encapsulation (the default) emulates the behavior of shadow DOM by preprocessing (and renaming) the CSS code to effectively scope the CSS to the component's view. For details, see Inspecting generated CSS below.

  • None means that Angular does no view encapsulation. Angular adds the CSS to the global styles. The scoping rules, isolations, and protections discussed earlier don't apply. This is essentially the same as pasting the component's styles into the HTML.

To set the components encapsulation mode, use the encapsulation property in the component metadata:

// warning: few browsers support shadow DOM encapsulation at this time
encapsulation: ViewEncapsulation.ShadowDom

ShadowDom view encapsulation only works on browsers that have native support for shadow DOM (see Shadow DOM v1 on the Can I use site). The support is still limited, which is why Emulated view encapsulation is the default mode and recommended in most cases.

Inspecting generated CSS

When using emulated view encapsulation, Angular preprocesses all component styles so that they approximate the standard shadow CSS scoping rules.

In the DOM of a running Angular application with emulated view encapsulation enabled, each DOM element has some extra attributes attached to it:

<hero-details _nghost-pmm-5>
    <h2 _ngcontent-pmm-5>Mister Fantastic</h2>
    <hero-team _ngcontent-pmm-5 _nghost-pmm-6>
      <h3 _ngcontent-pmm-6>Team</h3>
    </hero-team>
  </hero-detail>

There are two kinds of generated attributes:

  • An element that would be a shadow DOM host in native encapsulation has a generated _nghost attribute. This is typically the case for component host elements.
  • An element within a component's view has a _ngcontent attribute that identifies to which host's emulated shadow DOM this element belongs.

The exact values of these attributes aren't important. They are automatically generated and you never refer to them in application code. But they are targeted by the generated component styles, which are in the <head> section of the DOM:

[_nghost-pmm-5] {
    display: block;
    border: 1px solid black;
  }

  h3[_ngcontent-pmm-6] {
    background-color: white;
    border: 1px solid #777;
  }

These styles are post-processed so that each selector is augmented with _nghost or _ngcontent attribute selectors. These extra selectors enable the scoping rules described in this page.

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Licensed under the Creative Commons Attribution License 4.0.
https://angular.io/guide/view-encapsulation