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#219 Isolate styling with shadow dom #253

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#219 Isolate styling with shadow dom #253

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b41c8f6
Use shadow dom and inject style-link tag manually in there
robatwilliams Oct 24, 2025
7f859dc
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robatwilliams Oct 24, 2025
12422ce
Highlight styles file double meaning
robatwilliams Oct 24, 2025
b37993c
Consumers no longer need to manually import styles
robatwilliams Oct 24, 2025
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1 change: 0 additions & 1 deletion README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -22,7 +22,6 @@ You will need to import the following files to use the tech-carbon-estimator:

- main.js
- polyfill.js
- styles.css
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Seemed likely this needed to be removed, but I haven't seen it used - Dan, I guess you will when you try embedding it in the website.

With the style isolation, we are changing our ask of consumers from "include this in your global styles somewhere" to "put this file at /styles.css for us". Which is very rigid.

Perhaps we should allow the styles url to be given as a component attribute - including any path and cache-busting suffixes.

Having the whole bundled styles within the js bundle (so we can import it as a string rather than from a URL path) would eliminate the issue altogether, but then we're back into custom build system/tooling territory.

Why is it necessary to have separate sl-style and package-style? If we could have package-style be always used, we could specify it in styleUrl and simplify things a lot, and then do something else (e.g. style tag) for adaptations the demo page requires.


These files can be found under dist/tech-carbon-estimator when developing locally.

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27 changes: 24 additions & 3 deletions angular.json
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Expand Up @@ -21,8 +21,18 @@
"polyfills": ["zone.js"],
"tsConfig": "tsconfig.app.json",
"assets": ["src/favicon.ico"],
"styles": ["src/styles.css", "src/sl-styles.css"],
"scripts": []
"styles": [
{
"input": "src/styles.css",
"bundleName": "styles",
"inject": false
},
{
"input": "src/sl-styles.css",
"bundleName": "styles",
"inject": false
}
]
},
"configurations": {
"production": {
Expand All @@ -43,7 +53,18 @@
"npm-package": {
"index": {"input": "src/package-index.html", "output": "index.html"},
"assets": [],
"styles": ["src/styles.css", "src/package-styles.css"]
"styles": [
{
"input": "src/styles.css",
"bundleName": "styles",
"inject": false
},
{
"input": "src/package-styles.css",
"bundleName": "styles",
"inject": false
}
]
},
"development": {
"optimization": false,
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4 changes: 2 additions & 2 deletions src/app/tech-carbon-estimator/tech-carbon-estimator.component.spec.ts
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Expand Up @@ -90,8 +90,8 @@ describe('TechCarbonEstimatorComponent', () => {
it('should show the form by default', () => {
fixture.detectChanges();

const formElement = fixture.nativeElement.querySelector('carbon-estimator-form');
const assumptionsElement = fixture.nativeElement.querySelector('assumptions-and-limitation');
const formElement = fixture.nativeElement.shadowRoot.querySelector('carbon-estimator-form');
const assumptionsElement = fixture.nativeElement.shadowRoot.querySelector('assumptions-and-limitation');

expect(formElement).toBeTruthy();
expect(assumptionsElement).toBeFalsy();
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24 changes: 21 additions & 3 deletions src/app/tech-carbon-estimator/tech-carbon-estimator.component.ts
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@@ -1,4 +1,4 @@
import { ChangeDetectorRef, Component, ElementRef, Input, ViewChild } from '@angular/core';
import { ChangeDetectorRef, Component, ElementRef, Input, ViewChild, ViewEncapsulation } from '@angular/core';
import { CarbonEstimatorFormComponent } from '../carbon-estimator-form/carbon-estimator-form.component';
import { CarbonEstimationComponent } from '../carbon-estimation/carbon-estimation.component';
import { CarbonEstimation, EstimatorValues } from '../types/carbon-estimator';
Expand All @@ -24,6 +24,9 @@ import { TabItemComponent } from '../tab/tab-item/tab-item.component';
TabItemComponent,
],
templateUrl: './tech-carbon-estimator.component.html',

// Protect against style interference by the hosting page
encapsulation: ViewEncapsulation.ShadowDom
})
export class TechCarbonEstimatorComponent {
@Input() public extraHeight?: string;
Expand All @@ -35,8 +38,23 @@ export class TechCarbonEstimatorComponent {

constructor(
private estimationService: CarbonEstimationService,
private changeDetector: ChangeDetectorRef
) {}
private changeDetector: ChangeDetectorRef,
private ref: ElementRef
) {
this.insertShadowStylesLink()
}

private insertShadowStylesLink() {
// Reasons for this approach:
// 1. Angular global injection would insert the tag in the page root, so we disabled it.
// 2. Component `styleUrl` wouldn't allow us to vary stylesheets based on build configurations.

const link = document.createElement('link');
link.rel = 'stylesheet';
link.href = 'styles.css'; // This is the `bundleName` of the concatenated styles file

this.ref.nativeElement.shadowRoot.appendChild(link);
}

public handleFormSubmit(formValue: EstimatorValues) {
this.formValue = formValue;
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