chrome-devtools-frontend
Version:
Chrome DevTools UI
37 lines • 1.47 kB
JavaScript
/**
* @license
* Copyright (c) 2018 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 { AttributePart, directive } from '../lit-html.js';
const previousValues = new WeakMap();
/**
* For AttributeParts, sets the attribute if the value is defined and removes
* the attribute if the value is undefined.
*
* For other part types, this directive is a no-op.
*/
export const ifDefined = directive((value) => (part) => {
const previousValue = previousValues.get(part);
if (value === undefined && part instanceof AttributePart) {
// If the value is undefined, remove the attribute, but only if the value
// was previously defined.
if (previousValue !== undefined || !previousValues.has(part)) {
const name = part.committer.name;
part.committer.element.removeAttribute(name);
}
}
else if (value !== previousValue) {
part.setValue(value);
}
previousValues.set(part, value);
});
//# sourceMappingURL=if-defined.js.map