| 1 | 
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| 2 |
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| 3 | 
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| 4 | [](https://www.npmjs.com/package/async)
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| 5 | [](https://coveralls.io/r/caolan/async?branch=master)
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| 6 | [](https://gitter.im/caolan/async?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
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| 7 | [](https://www.jsdelivr.com/package/npm/async)
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| 8 |
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| 9 | <!--
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| 10 | |Linux|Windows|MacOS|
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| 11 | |-|-|-|
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| 12 | |[](https://dev.azure.com/caolanmcmahon/async/_build/latest?definitionId=1&branchName=master) | [](https://dev.azure.com/caolanmcmahon/async/_build/latest?definitionId=1&branchName=master) | [](https://dev.azure.com/caolanmcmahon/async/_build/latest?definitionId=1&branchName=master)| -->
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| 13 |
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| 14 | Async is a utility module which provides straight-forward, powerful functions for working with [asynchronous JavaScript](http://caolan.github.io/async/v3/global.html). Although originally designed for use with [Node.js](https://nodejs.org/) and installable via `npm i async`, it can also be used directly in the browser. An ESM/MJS version is included in the main `async` package that should automatically be used with compatible bundlers such as Webpack and Rollup.
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| 15 |
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| 16 | A pure ESM version of Async is available as [`async-es`](https://www.npmjs.com/package/async-es).
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| 17 |
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| 18 | For Documentation, visit <https://caolan.github.io/async/>
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| 19 |
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| 20 | *For Async v1.5.x documentation, go [HERE](https://github.com/caolan/async/blob/v1.5.2/README.md)*
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| 21 |
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| 22 |
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| 23 | ```javascript
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| 24 | // for use with Node-style callbacks...
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| 25 | var async = require("async");
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| 26 |
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| 27 | var obj = {dev: "/dev.json", test: "/test.json", prod: "/prod.json"};
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| 28 | var configs = {};
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| 29 |
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| 30 | async.forEachOf(obj, (value, key, callback) => {
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| 31 | fs.readFile(__dirname + value, "utf8", (err, data) => {
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| 32 | if (err) return callback(err);
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| 33 | try {
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| 34 | configs[key] = JSON.parse(data);
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| 35 | } catch (e) {
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| 36 | return callback(e);
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| 37 | }
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| 38 | callback();
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| 39 | });
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| 40 | }, err => {
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| 41 | if (err) console.error(err.message);
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| 42 | // configs is now a map of JSON data
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| 43 | doSomethingWith(configs);
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| 44 | });
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| 45 | ```
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| 46 |
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| 47 | ```javascript
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| 48 | var async = require("async");
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| 49 |
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| 50 | // ...or ES2017 async functions
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| 51 | async.mapLimit(urls, 5, async function(url) {
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| 52 | const response = await fetch(url)
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| 53 | return response.body
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| 54 | }, (err, results) => {
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| 55 | if (err) throw err
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| 56 | // results is now an array of the response bodies
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| 57 | console.log(results)
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| 58 | })
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| 59 | ```
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