@webcomponents/webcomponentsjs/src/platform/promise.js

Web Components Polyfills

/**
@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 PromisePolyfill from 'promise-polyfill/src/index.js';
/*
Assign the ES6 promise polyfill to window ourselves instead of using the "auto"
polyfill to work around
https://github.com/webcomponents/webcomponentsjs/issues/837
*/
if (!window.Promise) {
    window.Promise = PromisePolyfill;
    // save Promise API
    /* eslint-disable no-self-assign */
    // PromisePolyfill.prototype['catch'] = PromisePolyfill.prototype.catch;
    PromisePolyfill.prototype['then'] = PromisePolyfill.prototype.then;
    // PromisePolyfill.prototype['finally'] = PromisePolyfill.prototype.finally;
    PromisePolyfill['all'] = PromisePolyfill.all;
    PromisePolyfill['race'] = PromisePolyfill.race;
    PromisePolyfill['resolve'] = PromisePolyfill.resolve;
    PromisePolyfill['reject'] = PromisePolyfill.reject;
    /* eslint-enable */
    // approach copied from
    // https://github.com/Polymer/polymer/blob/v3.0.2/lib/utils/async.js
    const node = document.createTextNode('');
    const twiddleNode = function twiddleNode() {
        node.textContent = node.textContent.length > 0 ? '' : 'a';
    };
    /** @type {!Array<function():void>} */
    const callbacks = [];
    new MutationObserver(() => {
        const len = callbacks.length;
        for (let i = 0; i < len; i++) {
            callbacks[i]();
        }
        callbacks.splice(0, len);
    }).observe(node, { characterData: true });
    // set _immediateFn to a MutationObserver for close-to-native timing
    PromisePolyfill._immediateFn = (fn) => {
        callbacks.push(fn);
        twiddleNode();
    };
}
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