axax/esnext/concurrentMap.js

A library of async iterator extensions for JavaScript including ```map```, ```reduce```, ```filter```, ```flatMap```, ```pipe``` and [more](https://github.com/jamiemccrindle/axax/blob/master/docs/API.md#functions).

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
const deferred_1 = require("./deferred");
const subject_1 = require("./subject");
const toCallbacks_1 = require("./toCallbacks");
/**
 * Runs a mapping function over an asynchronous iterable
 */
function concurrentMap(mapper, concurrency) {
    return function inner(source) {
        const subject = new subject_1.Subject();
        let done = false;
        subject.finally(() => {
            done = true;
        });
        let running = 0;
        let deferred = new deferred_1.Deferred();
        toCallbacks_1.toCallbacks(result => {
            if (done) {
                throw new toCallbacks_1.StopError();
            }
            if (!result.done) {
                running += 1;
                if (running >= concurrency) {
                    deferred = new deferred_1.Deferred();
                }
                mapper(result.value).then(value => {
                    running -= 1;
                    subject.onNext(value);
                    if (running < concurrency) {
                        deferred.resolve();
                    }
                });
                return deferred.promise;
            }
            else {
                subject.onCompleted();
                return Promise.resolve();
            }
        })(source);
        return subject.iterator;
    };
}
exports.concurrentMap = concurrentMap;