初始化

康凯

2022-05-20 aa4c235a8ca67ea8b731f90c951a465e92c0a865

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'use strict';
module.exports = (iterable, mapper, opts) => new Promise((resolve, reject) => {
    opts = Object.assign({
        concurrency: Infinity
    }, opts);
 
    if (typeof mapper !== 'function') {
        throw new TypeError('Mapper function is required');
    }
 
    const concurrency = opts.concurrency;
 
    if (!(typeof concurrency === 'number' && concurrency >= 1)) {
        throw new TypeError(`Expected \`concurrency\` to be a number from 1 and up, got \`${concurrency}\` (${typeof concurrency})`);
    }
 
    const ret = [];
    const iterator = iterable[Symbol.iterator]();
    let isRejected = false;
    let iterableDone = false;
    let resolvingCount = 0;
    let currentIdx = 0;
 
    const next = () => {
        if (isRejected) {
            return;
        }
 
        const nextItem = iterator.next();
        const i = currentIdx;
        currentIdx++;
 
        if (nextItem.done) {
            iterableDone = true;
 
            if (resolvingCount === 0) {
                resolve(ret);
            }
 
            return;
        }
 
        resolvingCount++;
 
        Promise.resolve(nextItem.value)
            .then(el => mapper(el, i))
            .then(
                val => {
                    ret[i] = val;
                    resolvingCount--;
                    next();
                },
                err => {
                    isRejected = true;
                    reject(err);
                }
            );
    };
 
    for (let i = 0; i < concurrency; i++) {
        next();
 
        if (iterableDone) {
            break;
        }
    }
});