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eachAsync.js
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eachAsync.js
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'use strict';
/*!
* Module dependencies.
*/
const async = require('async');
const utils = require('../../utils');
/**
* Execute `fn` for every document in the cursor. If `fn` returns a promise,
* will wait for the promise to resolve before iterating on to the next one.
* Returns a promise that resolves when done.
*
* @param {Function} next the thunk to call to get the next document
* @param {Function} fn
* @param {Object} options
* @param {Function} [callback] executed when all docs have been processed
* @return {Promise}
* @api public
* @method eachAsync
*/
module.exports = function eachAsync(next, fn, options, callback) {
const parallel = options.parallel || 1;
const handleNextResult = function(doc, callback) {
const promise = fn(doc);
if (promise && typeof promise.then === 'function') {
promise.then(
function() { callback(null); },
function(error) { callback(error || new Error('`eachAsync()` promise rejected without error')); });
} else {
callback(null);
}
};
const iterate = function(callback) {
let drained = false;
const nextQueue = async.queue(function(task, cb) {
if (drained) {
return cb();
}
next(function(err, doc) {
if (err) return cb(err);
cb(null, doc);
});
}, 1);
const getAndRun = function(cb) {
nextQueue.push({}, function(err, doc) {
if (err) return cb(err);
if (drained) {
return;
}
if (doc == null) {
drained = true;
return callback(null);
}
handleNextResult(doc, function(err) {
if (err) return cb(err);
// Make sure to clear the stack re: gh-4697
setTimeout(function() {
getAndRun(cb);
}, 0);
});
});
};
let error = null;
for (let i = 0; i < parallel; ++i) {
getAndRun(err => {
if (error != null) {
return;
}
if (err != null) {
error = err;
return callback(err);
}
});
}
};
return utils.promiseOrCallback(callback, cb => {
iterate(cb);
});
};