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'use strict';
const AggregateError = require('aggregate-error');
module.exports = async (
iterable,
mapper,
{
concurrency = Infinity,
stopOnError = true
} = {}
) => {
return new Promise((resolve, reject) => {
if (typeof mapper !== 'function') {
throw new TypeError('Mapper function is required');
}
if (!((Number.isSafeInteger(concurrency) || concurrency === Infinity) && concurrency >= 1)) {
throw new TypeError(`Expected \`concurrency\` to be an integer from 1 and up or \`Infinity\`, got \`${concurrency}\` (${typeof concurrency})`);
}
const result = [];
const errors = [];
const iterator = iterable[Symbol.iterator]();
let isRejected = false;
let isIterableDone = false;
let resolvingCount = 0;
let currentIndex = 0;
const next = () => {
if (isRejected) {
return;
}
const nextItem = iterator.next();
const index = currentIndex;
currentIndex++;
if (nextItem.done) {
isIterableDone = true;
if (resolvingCount === 0) {
if (!stopOnError && errors.length !== 0) {
reject(new AggregateError(errors));
} else {
resolve(result);
}
}
return;
}
resolvingCount++;
(async () => {
try {
const element = await nextItem.value;
result[index] = await mapper(element, index);
resolvingCount--;
next();
} catch (error) {
if (stopOnError) {
isRejected = true;
reject(error);
} else {
errors.push(error);
resolvingCount--;
next();
}
}
})();
};
for (let i = 0; i < concurrency; i++) {
next();
if (isIterableDone) {
break;
}
}
});
};
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