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70 lines
2.5 KiB
70 lines
2.5 KiB
(function(exports) {
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"use strict";
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exports.batchAsync = function(limit, arr, doStuff) {
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arr = arr.slice(0);
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return new Promise(function(resolve, reject) {
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var total = arr.length;
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var active = 0;
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var results = [];
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var error;
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function doMoreStuff() {
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// Don't take on any more tasks if we've errored,
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// or if too many are already in progress
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if (error || active > limit) {
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return;
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}
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// If there are no more tasks to start, return
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if (!arr.length) {
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// If everything is also *finished*, resolve
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if (active < 1) {
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resolve(results);
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}
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return;
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}
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// We need to dequeue the task here so the index is correct
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// (keep in mind we want to support sync and async)
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var index = total - arr.length;
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var task = arr.shift();
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active += 1;
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// Spawn another task immediately,
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// which will be stopped if we're at the limit
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doMoreStuff();
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var p;
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try {
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p = doStuff(task, index, arr);
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} catch (e) {
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// we need to handle, and bubble, synchronous errors
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error = e;
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reject(e);
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throw e;
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}
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// Do stuff and then decrease the active counter when done
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// add support for sync by rapping in a promise
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Promise.resolve(p)
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.then(function(result) {
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if ("undefined" === typeof result) {
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throw new Error(
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"result was 'undefined'. Please return 'null' to signal that you didn't just forget to return another promise."
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);
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}
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active -= 1;
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results[index] = result;
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})
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.then(doMoreStuff)
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.catch(function(e) {
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// handle async errors
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error = e;
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reject(e);
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});
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}
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doMoreStuff();
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});
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};
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})("undefined" !== typeof window ? window : module.exports);
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