Promise Patterns

dist-index.js

// This file is generated by babel-plugin-transform-async-to-generator
function _asyncToGenerator(fn) { return function () { var gen = fn.apply(this, arguments); return new Promise(function (resolve, reject) { function step(key, arg) { try { var info = gen[key](arg); var value = info.value; } catch (error) { reject(error); return; } if (info.done) { resolve(value); } else { return Promise.resolve(value).then(function (value) { step("next", value); }, function (err) { step("throw", err); }); } } return step("next"); }); }; }

function foo() {
  var _this = this;
 
  return _asyncToGenerator(function* () {
    // Uses yield instead of await.
    return true;
  });
}

example-package.json

{
  // Entrypoint should be your shim file.
  "main": "index.js",
  // Include files that should be published.
  "files": [
    "index.js",
    "dist",
    "src"
  ],
  "dependencies": {
    "semver": "^5.4.1"
  },
  "devDependencies": {
    "babel-cli": "^6.24.1",
    "babel-core": "^6.25.0",
    "babel-plugin-transform-async-to-generator": "^6.24.1"
  },  
  // Now you can support any node version > 6.
  "engines": {
    "node": ">= 6.9.1"
  },
  // Add the build script and prepublish script
  "scripts": {
    "build": "babel src/ -d dist/",
    "prepublish": "yarn run build"
  }
}

index.js

const semver = require('semver');

let main;
if (semver.lt(process.version, '7.6.0')) {
  // Use built entrypoint for any version below 7.6.0 since
  // all other versions don't natively support async functions.
  // http://node.green/#ES2017-features-async-functions
  main = require('dist-index.js');
} else {
  main = require('src-index.js');
}
module.exports = main;

migrate-module.js

// Automatically set up your project to be transpiled using:
// node migrate-module.js <src-dir>
const fs = require('fs');

const srcFolder = process.argv[2];

if (!srcFolder) {
  console.log('Please provide the name of your src folder.');
  process.exit(1);
}

const raw = fs.readFileSync('./package.json');
const pkg = JSON.parse(raw);

pkg.main = 'index.js';

if (!pkg.engines) pkg.engines = {};
pkg.engines.node = '>= 6.9.1';

if (!pkg.scripts) pkg.scripts = {};
pkg.scripts.babelBuild = `babel ${srcFolder} -d dist`;

const buildCmd = 'yarn run babelBuild';
if (pkg.scripts.prepublish) {
  pkg.scripts.prepublish = buildCmd + ' && ' + pkg.scripts.prepublish;
} else {
  pkg.scripts.prepublish = buildCmd;
}

// Explicitly add build files
if (!pkg.files) pkg.files = [];
pkg.files.push('index.js', 'src', 'dist');

fs.writeFileSync('package.json', JSON.stringify(pkg, null, 2));
process.exit(0);

promise-all.js

// Handle lists with Promise.all and Array.map
async function addToList(emails) {
  await Promise.all(emails.map(async (email) => {
    const valid = await validate(email);
    if (!valid) return;

    await db.list.insert({ email });
    return email;
  }));
}

promise-callbacks.js

// Promisify just one call.
const { deferred } = require('promise-callbacks');

function bar() {
  const promise = deferred();
  doAsync(promise.defer());
  return promise;
}

// Promisify whole apis.
const { promisify } = require('promise-callbacks');

const api = {
  doAsync: (cb) => {},
  doMoreAsync: (cb) => {}
};

const doPromisified = promisify.all(api);
doPromisified.doAsync.then(() => {
  // Celebrate
});

promise-iterate.js

// Any iterator with a next method will do.
class Iterator {
  next() {
    if (!this.results) this.results = this.get();

    return results.pop();
  }
}

// Use promise iterate to defer async calls to the iterator without
// loading all results at once.
const { promiseIterate } = require('promise-iterate');

async function sendToEveryone(names) {
  const cursor = new Iterator();

  await promiseIterate(cursor, async (contact) => {
    await sendEmail(contact.firstName, 'Hello!');
  });

  return true;
}

promise-pool.js

// Use promise pool for arbitrary length data to limit memory usage 
// and active requests.
const PromisePool = require('@mixmaxhq/promise-pool');

async function bulkSend(names) {
  const pool = new PromisePool(10);

  for (let i = 0; i < names.length; i++) {
    const name = names[i];
    await pool.start(async () => {
      send(name, 'Hello!');
    });
  }

  await pool.flush();
  return { message: 'success' };
}

src-index.js

async function foo() {
 // Some async action.
 return true;
}

module.exports = {
  foo
};