@polymer/lit-element
Version:
Polymer based lit-html custom element
43 lines • 1.78 kB
JavaScript
/**
@license
Copyright (c) 2019 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
*/
export const supportsAdoptingStyleSheets = ('adoptedStyleSheets' in Document.prototype);
export class CSSResult {
constructor(cssText) { this.cssText = cssText; }
// Note, this is a getter so that it's lazy. In practice, this means
// stylesheets are not created until the first element instance is made.
get styleSheet() {
if (this._styleSheet === undefined) {
// Note, if `adoptedStyleSheets` is supported then we assume CSSStyleSheet
// is constructable.
if (supportsAdoptingStyleSheets) {
this._styleSheet = new CSSStyleSheet();
this._styleSheet.replaceSync(this.cssText);
}
else {
this._styleSheet = null;
}
}
return this._styleSheet;
}
}
const textFromCSSResult = (value) => {
if (value instanceof CSSResult) {
return value.cssText;
}
else {
throw new Error(`Value passed to 'css' function must be a 'css' function result: ${value}.`);
}
};
export const css = (strings, ...values) => {
const cssText = values.reduce((acc, v, idx) => acc + textFromCSSResult(v) + strings[idx + 1], strings[0]);
return new CSSResult(cssText);
};
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