| // Copyright 2018 Google LLC |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // https://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| |
| /** @module elements-sk/define */ |
| |
| /** |
| * Define a custom element definition. It will only define a tag name once |
| * and will log an error if there's an attempt to define a tag name a second |
| * time. This is useful for tests since you can't undefine a custom element. |
| * |
| * See also https://github.com/karma-runner/karma/issues/412 |
| * |
| * @param tagName - The name of the tag. |
| * @param cl - The class for the given tag. |
| * |
| * @example |
| * |
| * Instead of: |
| * |
| * window.customElements.define('my-element', class extends HTMLElement {...}); |
| * |
| * Use: |
| * |
| * import { define } from 'elements-sk/define' |
| * define('my-element', class extends HTMLElement {...}); |
| * |
| */ |
| export function define(tagName: string, cl: CustomElementConstructor): void { |
| if (window.customElements.get(tagName) === undefined) { |
| window.customElements.define(tagName, cl); |
| } else { |
| console.log( |
| `Multiple registration attempts for ${tagName}. ` + |
| 'This should only happen during testing, ' + |
| "it's probably an error outside of testing." |
| ); |
| } |
| } |