aaac7fed
 liuqimichale
add
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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;
}
}
});
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