for batching async tasks
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(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);
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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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@ -0,0 +1,25 @@
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{
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"name": "batchasync",
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"version": "1.0.0",
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"description": "Like forEachAsync, or Promise.all(), but handling a bounded number of items at any given time.",
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"main": "batchasync.js",
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"scripts": {
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"test": "node ./test.js"
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},
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"repository": {
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"type": "git",
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"url": "https://git.coolaj86.com/coolaj86/batchasync.js.git"
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},
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"keywords": [
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"batch",
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"forEach",
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"async",
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"forEachAsync",
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"Promise.all",
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"Promise",
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"task",
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"queue"
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],
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"author": "AJ ONeal <coolaj86@gmail.com> (https://coolaj86.com/)",
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"license": "MPL-2.0"
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}
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(function (exports) {
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'use strict';
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var batchAsync = exports.batchAsync || require('./batchasync.js').batchAsync;
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function testBatch() {
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var timeouts = [100, 80, 20, 500, 50, 30, 200, 300];
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var tasks = timeouts.map(function(timeout, i) {
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return function() {
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return promiseTimeout(timeout).then(function() {
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console.log('task:', i, timeouts[i]);
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return i;
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});
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};
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});
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var len = tasks.length;
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return batchAsync(4, tasks, function(task) {
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return task();
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})
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.then(function(results) {
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console.info('results:', results);
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if (len !== results.length) {
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throw new Error('result set too small');
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}
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if (results.join(' ') !== results.sort().join(' ')) {
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throw new Error('result set out-of-order');
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}
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})
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.then(function() {
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return batchAsync(4, [], 'not a function').then(function() {
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console.info('Handled ZERO tasks correctly.');
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});
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})
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.then(function() {
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return batchAsync(4, timeouts, function(x) {
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return x;
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}).then(function(results) {
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if (results.join(' ') !== timeouts.join(' ')) {
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console.error(results);
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throw new Error('sync result set out-of-order');
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}
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console.info('Handled sync tasks correctly.');
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});
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})
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.then(function() {
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return batchAsync(4, tasks, function(task) {
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if (0 === Math.floor(Math.random() * 2) % 2) {
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throw new Error('any async error will do');
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}
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return task();
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})
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.then(function(results) {
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console.log(results);
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var e = new Error('async rejection should not pass!');
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e.FAIL = true;
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throw e;
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})
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.catch(function(e) {
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if (e.FAIL) {
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throw e;
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}
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console.info('Pass: Exception thrown when expected');
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});
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})
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.then(function() {
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return batchAsync(4, timeouts, function() {
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if (0 === Math.floor(Math.random() * 2) % 2) {
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throw new Error('any sync error will do');
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}
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return null;
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})
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.then(function(results) {
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var e = new Error('should not pass sync exception!');
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e.FAIL = true;
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throw e;
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})
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.catch(function(e) {
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if (e.FAIL) {
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throw e;
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}
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})
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.then(function() {
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// wait for the tasks the error left dangling to print their message
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console.info('Pass: Promise rejected when expected');
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return promiseTimeout(1000);
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});
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});
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}
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function promiseTimeout(timeout) {
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return new Promise(function(resolve, reject) {
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setTimeout(resolve, timeout);
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});
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}
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testBatch()
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.then(function() {
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console.info('PROBABLY PASSED');
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console.info(
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'We tested what could be tested without knowing Passed what could be tested Do the results make sense?'
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);
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})
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.catch(function(e) {
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console.error('FAIL!');
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console.error(e);
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process.exit(500);
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});
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}('undefined' !== typeof window ? window : module.exports));
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