@apollo/client/utilities/observables/asyncMap.js

A fully-featured caching GraphQL client.

import { Observable } from "./Observable.js";
export function asyncMap(observable, mapFn, catchFn) {
    return new Observable(function (observer) {
        var next = observer.next, error = observer.error, complete = observer.complete;
        var activeCallbackCount = 0;
        var completed = false;
        var promiseQueue = {
            then: function (callback) {
                return new Promise(function (resolve) { return resolve(callback()); });
            },
        };
        function makeCallback(examiner, delegate) {
            if (examiner) {
                return function (arg) {
                    ++activeCallbackCount;
                    var both = function () { return examiner(arg); };
                    promiseQueue = promiseQueue.then(both, both).then(function (result) {
                        --activeCallbackCount;
                        next && next.call(observer, result);
                        if (completed) {
                            handler.complete();
                        }
                    }, function (error) {
                        --activeCallbackCount;
                        throw error;
                    }).catch(function (caught) {
                        error && error.call(observer, caught);
                    });
                };
            }
            else {
                return function (arg) { return delegate && delegate.call(observer, arg); };
            }
        }
        var handler = {
            next: makeCallback(mapFn, next),
            error: makeCallback(catchFn, error),
            complete: function () {
                completed = true;
                if (!activeCallbackCount) {
                    complete && complete.call(observer);
                }
            },
        };
        var sub = observable.subscribe(handler);
        return function () { return sub.unsubscribe(); };
    });
}
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