All files / src/util once.ts

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/**
 * Copyright 2017-2020 Plexus Interop Deutsche Bank AG
 * SPDX-License-Identifier: Apache-2.0
 *
 * 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.
 */
/**
 * Call source fn only once, even if source promise is rejected
 */
export const once = <Req, Res>(fn: (req?: Req) => Promise<Res>): (req?: Req) => Promise<Res> => {
    let promise: Promise<Res> | undefined;
    return (req?: Req) => {
        if (!promise) {
            promise = fn(req);
        }
        return promise;
    };
};
 
export function onceVoid(fn: () => void): () => void {
    let called = false;
    return () => {
        if (!called) {
            called = true;
            fn();
        }
    };
}