feat: experimental fastboot support

Only works in Chrome 85+ with an experimental flag, see https://web.dev/declarative-shadow-dom/

addon/components/shadow-dom/component.js

@@ -2,11 +2,14 @@ import Component from '@glimmer/component';
 import { tracked } from '@glimmer/tracking';
 import { action } from '@ember/object';
 
+const isFastBoot = typeof FastBoot !== 'undefined';
+
 export default class ShadowDom extends Component {
   @tracked shadow = null;
   @tracked tagName = 'div';
 
   defaultMode = 'open';
+  isFastBoot = isFastBoot;
 
   constructor() {
     super(...arguments);
@@ -18,6 +21,6 @@ export default class ShadowDom extends Component {
     let mode = this.args.mode || this.defaultMode;
     let shadow = element.attachShadow({ mode });
 
-		this.shadow = shadow;
+    this.shadow = shadow;
   }
 }

app/templates/components/shadow-dom.hbs

@@ -1,12 +1,18 @@
 {{#let (element this.tagName) as |Tag|}}
-  <Tag
-    {{did-insert this.setupRoot}}
-    ...attributes
-  />
-{{/let}}
+  {{#if this.isFastBoot}}
+    <Tag ...attributes>
+      <template shadowroot={{@mode}}>
+        <slot></slot>
+      </template>
+      {{yield}}
+    </Tag>
+  {{else}}
+    <Tag ...attributes {{did-insert this.setupRoot}} />
 
-{{#if this.shadow}}
-  {{#-in-element this.shadow}}
-    {{yield}}
-  {{/-in-element}}
-{{/if}}
+    {{#if this.shadow}}
+      {{#-in-element this.shadow}}
+        {{yield}}
+      {{/-in-element}}
+    {{/if}}
+  {{/if}}
+{{/let}}

package.json

@@ -27,22 +27,22 @@
     "release": "standard-version"
   },
   "dependencies": {
-    "@ember/render-modifiers": "^1.0.0",
+    "@ember/render-modifiers": "^1.0.2",
     "@glimmer/component": "^1.0.0",
+    "@glimmer/tracking": "^1.0.1",
     "ember-cli-babel": "^7.22.1",
     "ember-cli-htmlbars": "^5.3.1",
     "ember-element-helper": "^0.3.1"
   },
   "devDependencies": {
     "@ember/optional-features": "^2.0.0",
-    "@glimmer/component": "^1.0.1",
-    "@glimmer/tracking": "^1.0.1",
     "babel-eslint": "^10.1.0",
     "broccoli-asset-rev": "^3.0.0",
     "ember-auto-import": "^1.6.0",
     "ember-cli": "^3.21.2",
     "ember-cli-app-version": "^3.2.0",
     "ember-cli-dependency-checker": "^3.2.0",
+    "ember-cli-fastboot": "^2.2.3",
     "ember-cli-inject-live-reload": "^2.0.2",
     "ember-cli-sri": "^2.1.1",
     "ember-cli-terser": "^4.0.0",