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