lit-element.js

/**
 * @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 { TemplateResult } from '/node_modules/lit-html/lit-html.js';
import { render } from '/node_modules/lit-html/lib/shady-render.js';
import { UpdatingElement } from './lib/updating-element.js';
export * from './lib/updating-element.js';
export * from './lib/decorators.js';
export { html, svg, TemplateResult, SVGTemplateResult } from '/node_modules/lit-html/lit-html.js';
import { supportsAdoptingStyleSheets } from './lib/css-tag.js';
export * from './lib/css-tag.js';
// IMPORTANT: do not change the property name or the assignment expression.
// This line will be used in regexes to search for LitElement usage.
// TODO(justinfagnani): inject version number at build time
(window['litElementVersions'] || (window['litElementVersions'] = []))
    .push('2.0.1');
/**
 * Minimal implementation of Array.prototype.flat
 * @param arr the array to flatten
 * @param result the accumlated result
 */
function arrayFlat(styles, result = []) {
    for (let i = 0, length = styles.length; i < length; i++) {
        const value = styles[i];
        if (Array.isArray(value)) {
            arrayFlat(value, result);
        }
        else {
            result.push(value);
        }
    }
    return result;
}
/** Deeply flattens styles array. Uses native flat if available. */
const flattenStyles = (styles) => styles.flat ? styles.flat(Infinity) : arrayFlat(styles);
export class LitElement extends UpdatingElement {
    /** @nocollapse */
    static finalize() {
        super.finalize();
        // Prepare styling that is stamped at first render time. Styling
        // is built from user provided `styles` or is inherited from the superclass.
        this._styles =
            this.hasOwnProperty(JSCompiler_renameProperty('styles', this)) ?
                this._getUniqueStyles() :
                this._styles || [];
    }
    /** @nocollapse */
    static _getUniqueStyles() {
        // Take care not to call `this.styles` multiple times since this generates
        // new CSSResults each time.
        // TODO(sorvell): Since we do not cache CSSResults by input, any
        // shared styles will generate new stylesheet objects, which is wasteful.
        // This should be addressed when a browser ships constructable
        // stylesheets.
        const userStyles = this.styles;
        const styles = [];
        if (Array.isArray(userStyles)) {
            const flatStyles = flattenStyles(userStyles);
            // As a performance optimization to avoid duplicated styling that can
            // occur especially when composing via subclassing, de-duplicate styles
            // preserving the last item in the list. The last item is kept to
            // try to preserve cascade order with the assumption that it's most
            // important that last added styles override previous styles.
            const styleSet = flatStyles.reduceRight((set, s) => {
                set.add(s);
                // on IE set.add does not return the set.
                return set;
            }, new Set());
            // Array.from does not work on Set in IE
            styleSet.forEach((v) => styles.unshift(v));
        }
        else if (userStyles) {
            styles.push(userStyles);
        }
        return styles;
    }
    /**
     * Performs element initialization. By default this calls `createRenderRoot`
     * to create the element `renderRoot` node and captures any pre-set values for
     * registered properties.
     */
    initialize() {
        super.initialize();
        this.renderRoot = this.createRenderRoot();
        // Note, if renderRoot is not a shadowRoot, styles would/could apply to the
        // element's getRootNode(). While this could be done, we're choosing not to
        // support this now since it would require different logic around de-duping.
        if (window.ShadowRoot && this.renderRoot instanceof window.ShadowRoot) {
            this.adoptStyles();
        }
    }
    /**
     * Returns the node into which the element should render and by default
     * creates and returns an open shadowRoot. Implement to customize where the
     * element's DOM is rendered. For example, to render into the element's
     * childNodes, return `this`.
     * @returns {Element|DocumentFragment} Returns a node into which to render.
     */
    createRenderRoot() {
        return this.attachShadow({ mode: 'open' });
    }
    /**
     * Applies styling to the element shadowRoot using the `static get styles`
     * property. Styling will apply using `shadowRoot.adoptedStyleSheets` where
     * available and will fallback otherwise. When Shadow DOM is polyfilled,
     * ShadyCSS scopes styles and adds them to the document. When Shadow DOM
     * is available but `adoptedStyleSheets` is not, styles are appended to the
     * end of the `shadowRoot` to [mimic spec
     * behavior](https://wicg.github.io/construct-stylesheets/#using-constructed-stylesheets).
     */
    adoptStyles() {
        const styles = this.constructor._styles;
        if (styles.length === 0) {
            return;
        }
        // There are three separate cases here based on Shadow DOM support.
        // (1) shadowRoot polyfilled: use ShadyCSS
        // (2) shadowRoot.adoptedStyleSheets available: use it.
        // (3) shadowRoot.adoptedStyleSheets polyfilled: append styles after
        // rendering
        if (window.ShadyCSS !== undefined && !window.ShadyCSS.nativeShadow) {
            window.ShadyCSS.ScopingShim.prepareAdoptedCssText(styles.map((s) => s.cssText), this.localName);
        }
        else if (supportsAdoptingStyleSheets) {
            this.renderRoot.adoptedStyleSheets =
                styles.map((s) => s.styleSheet);
        }
        else {
            // This must be done after rendering so the actual style insertion is done
            // in `update`.
            this._needsShimAdoptedStyleSheets = true;
        }
    }
    connectedCallback() {
        super.connectedCallback();
        // Note, first update/render handles styleElement so we only call this if
        // connected after first update.
        if (this.hasUpdated && window.ShadyCSS !== undefined) {
            window.ShadyCSS.styleElement(this);
        }
    }
    /**
     * Updates the element. This method reflects property values to attributes
     * and calls `render` to render DOM via lit-html. Setting properties inside
     * this method will *not* trigger another update.
     * * @param _changedProperties Map of changed properties with old values
     */
    update(changedProperties) {
        super.update(changedProperties);
        const templateResult = this.render();
        if (templateResult instanceof TemplateResult) {
            this.constructor
                .render(templateResult, this.renderRoot, { scopeName: this.localName, eventContext: this });
        }
        // When native Shadow DOM is used but adoptedStyles are not supported,
        // insert styling after rendering to ensure adoptedStyles have highest
        // priority.
        if (this._needsShimAdoptedStyleSheets) {
            this._needsShimAdoptedStyleSheets = false;
            this.constructor._styles.forEach((s) => {
                const style = document.createElement('style');
                style.textContent = s.cssText;
                this.renderRoot.appendChild(style);
            });
        }
    }
    /**
     * Invoked on each update to perform rendering tasks. This method must return
     * a lit-html TemplateResult. Setting properties inside this method will *not*
     * trigger the element to update.
     */
    render() {
    }
}
/**
 * Ensure this class is marked as `finalized` as an optimization ensuring
 * it will not needlessly try to `finalize`.
 */
LitElement.finalized = true;
/**
 * Render method used to render the lit-html TemplateResult to the element's
 * DOM.
 * @param {TemplateResult} Template to render.
 * @param {Element|DocumentFragment} Node into which to render.
 * @param {String} Element name.
 * @nocollapse
 */
LitElement.render = render;
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