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Add support for "private" custom elements #1943

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Merged
justinfagnani merged 1 commit into from
Jun 9, 2021
Merged

Add support for "private" custom elements #1943

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16 changes: 9 additions & 7 deletions packages/reactive-element/src/decorators/custom-element.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -12,11 +12,13 @@
*/
import {Constructor, ClassDescriptor} from './base.js';

const legacyCustomElement = (
tagName: string,
clazz: Constructor<HTMLElement>
) => {
window.customElements.define(tagName, clazz);
/**
* Allow for custom element classes with private constructors
*/
type CustomElementClass = Omit<typeof HTMLElement, 'new'>;

const legacyCustomElement = (tagName: string, clazz: CustomElementClass) => {
window.customElements.define(tagName, clazz as CustomElementConstructor);
// Cast as any because TS doesn't recognize the return type as being a
// subtype of the decorated class when clazz is typed as
// `Constructor<HTMLElement>` for some reason.
Expand Down Expand Up @@ -57,7 +59,7 @@ const standardCustomElement = (
*/
export const customElement =
(tagName: string) =>
(classOrDescriptor: Constructor<HTMLElement> | ClassDescriptor) =>
(classOrDescriptor: CustomElementClass | ClassDescriptor) =>
typeof classOrDescriptor === 'function'
? legacyCustomElement(tagName, classOrDescriptor)
: standardCustomElement(tagName, classOrDescriptor);
: standardCustomElement(tagName, classOrDescriptor as ClassDescriptor);
11 changes: 11 additions & 0 deletions packages/reactive-element/src/test/decorators/customElement_test.ts
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Expand Up @@ -16,4 +16,15 @@ suite('@customElement', () => {
const DefinedC = customElements.get(tagName);
assert.strictEqual(DefinedC, C0);
});
test('elements with private constructors can be defined', () => {
const tagName = generateElementName();
@customElement(tagName)
class C1 extends HTMLElement {
private constructor() {
super();
}
}
const DefinedC = customElements.get(tagName);
assert.strictEqual(DefinedC, C1);
});
});