ix/asynciterable/reduce.mjs

The Interactive Extensions for JavaScript

import { __asyncValues, __awaiter } from "tslib";
import { wrapWithAbort } from './operators/withabort.mjs';
import { throwIfAborted } from '../aborterror.mjs';
/**
 * Applies an accumulator function over an async-iterable sequence, returning the result of the aggregation as a
 * single element in the result sequence. The seed value, if specified, is used as the initial accumulator value.
 * For aggregation behavior with incremental intermediate results, scan.
 *
 * @template T The type of the elements in the source sequence.
 * @template R The type of the result of the aggregation.
 * @param {AsyncIterable<T>} source An async-iterable sequence to aggregate over.
 * @param {ReduceOptions<T, R>} options The options which contains a callback, with optional seedn and an optional abort signal for cancellation.
 * @returns {Promise<R>} A promise with the final accumulator value.
 */
export function reduce(source, options) {
    var _a, e_1, _b, _c;
    return __awaiter(this, void 0, void 0, function* () {
        const { ['seed']: seed, ['signal']: signal, ['callback']: callback } = options;
        const hasSeed = options.hasOwnProperty('seed');
        throwIfAborted(signal);
        let i = 0;
        let hasValue = false;
        let acc = seed;
        try {
            for (var _d = true, _e = __asyncValues(wrapWithAbort(source, signal)), _f; _f = yield _e.next(), _a = _f.done, !_a; _d = true) {
                _c = _f.value;
                _d = false;
                const item = _c;
                if (hasValue || (hasValue = hasSeed)) {
                    acc = yield callback(acc, item, i++, signal);
                }
                else {
                    acc = item;
                    hasValue = true;
                    i++;
                }
            }
        }
        catch (e_1_1) { e_1 = { error: e_1_1 }; }
        finally {
            try {
                if (!_d && !_a && (_b = _e.return)) yield _b.call(_e);
            }
            finally { if (e_1) throw e_1.error; }
        }
        if (!(hasSeed || hasValue)) {
            throw new Error('Sequence contains no elements');
        }
        return acc;
    });
}

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