material-motion/dist/combineLatest.js

Makes it easy to add rich, interactive motion to your application.

/** @license
 *  Copyright 2016 - present The Material Motion Authors. All Rights Reserved.
 *
 *  Licensed under the Apache License, Version 2.0 (the "License"); you may not
 *  use this file except in compliance with the License. You may obtain a copy
 *  of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 *  License for the specific language governing permissions and limitations
 *  under the License.
 */
import { MotionObservable, } from './observables/proxies';
import { isIterable, isObservable, } from './typeGuards';
export function combineLatest(streams, { waitForAllValues = true } = {}) {
    return new MotionObservable((observer) => {
        const outstandingKeys = new Set(Object.keys(streams));
        let nextValue;
        if (isIterable(streams)) {
            nextValue = [];
        }
        else {
            nextValue = {};
        }
        const subscriptions = {};
        let initializing = true;
        outstandingKeys.forEach(checkKey);
        initializing = false;
        // TypeScript doesn't know whether the index signature for `streams` (and
        // hence, `nextValue` and `outstandingKeys`) is a string or a number.
        // Thus, it throws an error at a simple `streams[key]`.  Since we know
        // that whichever it is, `key` can index into all three collections, we
        // cast each to `Dict<V>` and `key` to `string`.  Then, TypeScript will
        // happily index into the collections using `key`.
        function checkKey(key) {
            const maybeStream = streams[key];
            if (isObservable(maybeStream)) {
                subscriptions[key] = maybeStream.subscribe((value) => {
                    outstandingKeys.delete(key);
                    nextValue[key] = value;
                    emitNextValue();
                });
            }
            else {
                outstandingKeys.delete(key);
                nextValue[key] = maybeStream;
                emitNextValue();
            }
        }
        function emitNextValue() {
            if (waitForAllValues ? outstandingKeys.size === 0 : !initializing) {
                observer.next((Array.isArray(nextValue)
                    ? [...nextValue]
                    : Object.assign({}, nextValue)));
            }
        }
        emitNextValue();
        return function disconnect() {
            Object.values(subscriptions).forEach(subscription => subscription.unsubscribe());
        };
    });
}
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