lit-html/lib/render.js

HTML template literals in JavaScript

/**
 * @license
 * Copyright (c) 2017 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 { isCEPolyfill, removeNodes } from './dom.js';
import { templateFactory as defaultTemplateFactory } from './template-factory.js';
import { TemplateInstance } from './template-instance.js';
export const templateInstances = new WeakMap();
/**
 * Renders a template to a container.
 *
 * To update a container with new values, reevaluate the template literal and
 * call `render` with the new result.
 *
 * @param result a TemplateResult created by evaluating a template tag like
 *     `html` or `svg`.
 * @param container A DOM parent to render to. The entire contents are either
 *     replaced, or efficiently updated if the same result type was previous
 *     rendered there.
 * @param templateFactory a function to create a Template or retreive one from
 *     cache.
 */
export function render(result, container, templateFactory = defaultTemplateFactory) {
    const template = templateFactory(result);
    let instance = templateInstances.get(container);
    // Repeat render, just call update()
    if (instance !== undefined && instance.template === template &&
        instance.processor === result.processor) {
        instance.update(result.values);
        return;
    }
    // First render, create a new TemplateInstance and append it
    instance = new TemplateInstance(template, result.processor, templateFactory);
    templateInstances.set(container, instance);
    const fragment = instance._clone();
    removeNodes(container, container.firstChild);
    // Since we cloned in the polyfill case, now force an upgrade
    if (isCEPolyfill && !container.isConnected) {
        document.adoptNode(fragment);
        customElements.upgrade(fragment);
    }
    container.appendChild(fragment);
    instance.update(result.values);
}
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