chrome-devtools-frontend
Version:
Chrome DevTools UI
53 lines (45 loc) • 2 kB
text/typescript
/**
* @license
* Copyright (c) 2020 The Polymer Project Authors. All rights reserved.
* This code may only be used under the BSD style license found at
* http://polymer.github.io/LICENSE.txt
* The complete set of authors may be found at
* http://polymer.github.io/AUTHORS.txt
* The complete set of contributors may be found at
* http://polymer.github.io/CONTRIBUTORS.txt
* Code distributed by Google as part of the polymer project is also
* subject to an additional IP rights grant found at
* http://polymer.github.io/PATENTS.txt
*/
import {directive, NodePart, Part} from '../lit-html.js';
interface PreviousValue {
readonly template: HTMLTemplateElement;
readonly fragment: DocumentFragment;
}
// For each part, remember the value that was last rendered to the part by the
// templateContent directive, and the DocumentFragment that was last set as a
// value. The DocumentFragment is used as a unique key to check if the last
// value rendered to the part was with templateContent. If not, we'll always
// re-render the value passed to templateContent.
const previousValues = new WeakMap<NodePart, PreviousValue>();
/**
* Renders the content of a template element as HTML.
*
* Note, the template should be developer controlled and not user controlled.
* Rendering a user-controlled template with this directive
* could lead to cross-site-scripting vulnerabilities.
*/
export const templateContent =
directive((template: HTMLTemplateElement) => (part: Part): void => {
if (!(part instanceof NodePart)) {
throw new Error('templateContent can only be used in text bindings');
}
const previousValue = previousValues.get(part);
if (previousValue !== undefined && template === previousValue.template &&
part.value === previousValue.fragment) {
return;
}
const fragment = document.importNode(template.content, true);
part.setValue(fragment);
previousValues.set(part, {template, fragment});
});