ix/asynciterable/reduceright.js

The Interactive Extensions for JavaScript

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.reduceRight = void 0;
const tslib_1 = require("tslib");
const toarray_js_1 = require("./toarray.js");
const aborterror_js_1 = require("../aborterror.js");
/**
 * Applies an accumulator function over an async-iterable sequence from the end, 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 from the right.
 * @param {ReduceOptions<T, R>} options The options which contains a callback, with optional seed and an optional abort signal for cancellation.
 * @returns {Promise<R>} A promise with the final accumulator value.
 */
function reduceRight(source, options) {
    return tslib_1.__awaiter(this, void 0, void 0, function* () {
        const { ['seed']: seed, ['signal']: signal, ['callback']: callback } = options;
        const hasSeed = options.hasOwnProperty('seed');
        (0, aborterror_js_1.throwIfAborted)(signal);
        const array = yield (0, toarray_js_1.toArray)(source, signal);
        let hasValue = false;
        let acc = seed;
        for (let offset = array.length - 1; offset >= 0; offset--) {
            const item = array[offset];
            if (hasValue || (hasValue = hasSeed)) {
                acc = yield callback(acc, item, offset, signal);
            }
            else {
                acc = item;
                hasValue = true;
            }
        }
        if (!(hasSeed || hasValue)) {
            throw new Error('Sequence contains no elements');
        }
        return acc;
    });
}
exports.reduceRight = reduceRight;

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