simple-email/node_modules/async/README.md

Async is a utility module which provides straight-forward, powerful functions for working with asynchronous JavaScript. Although originally designed for use with Node.js and installable via npm install --save async, it can also be used directly in the browser.

This version of the package is optimized for the Node.js environment. If you use Async with webpack, install async-es instead.

For Documentation, visit https://caolan.github.io/async/

For Async v1.5.x documentation, go HERE

// for use with Node-style callbacks...
var async = require("async");
var obj = {dev: "/dev.json", test: "/test.json", prod: "/prod.json"};
var configs = {};
async.forEachOf(obj, (value, key, callback) => {
fs.readFile(__dirname + value, "utf8", (err, data) => {
if (err) return callback(err);
try {
configs[key] = JSON.parse(data);
} catch (e) {
return callback(e);
}
callback();
});
}, err => {
if (err) console.error(err.message);
// configs is now a map of JSON data
    doSomethingWith(configs);
});

var async = require("async");
// ...or ES2017 async functions
async.mapLimit(urls, 5, async function(url) {
const response = await fetch(url)
return response.body
}, (err, results) => {
if (err) throw err
// results is now an array of the response bodies
    console.log(results)
})